Investigating the drivers of methane release from cold seeps on the Southern Hydrate Ridge off the coast of Oregon.

Cold seeps release methane along most coastal margins, either as gas dissolved in water or as bubbles which rise through the water column. Bubbles of methane released from cold seeps have been observed rising hundreds of meters through the water column in the Guaymas Basin in the Gulf of California, on the continental rise off the coast of the Carolinas, along the Cascadia Margin off the coast of British Colombia and the northwestern US, in the Okinawa Trough in the East China Sea, in the Black Sea, and in the Gulf of Mexico, as well as at an experimental station in Monterey Bay. When emitted at depths of less than a hundred metres, methane bubbles typically reach the surface and release their gas into the atmosphere, while bubbles released at greater depths the methane in them is lost into the water column as they rise. However, in areas where stable gas hydrates exist at deeper depths, then the bubbles may have a hydrate coating, which slows dissolution of their gas content, allowing bubbles from greater depths to reach the surface. 

This gas is thought to be of minor significance compared to other sources of carbon entering the atmosphere, but the amount gas produced, and how this varies both geographically and over time, has been the subject of very little investigation. The amount of gas released at different sites is known to vary considerably, which is thought to be related to factors such as the subsurface structure and the source of the methane. External factors are also thought to affect the amount of methane being released, such as variations in hydrostatic pressure caused by the action of tides, swell, or storms, changes in sea temperature linked to seasons or longer term changes, seismic tremors, and even to isostatic rebound.

Hydrate Ridge forms part of the Cascadia Subduction Zone, an anticlinal ridge on the accretionary wedge with a north-south orientation. This ridge has two distinct areas of cold seeps, known as the Northern and Southern Hydrate Ridges, both of which have extremely large methane hydrate deposits close to the sediment surface, which lead to persistent gas emissions in the form of bubble plumes, as well as extensive chemosynthetic ecosystems and authigenic carbonates. Seismic profiling of the Southern Hydrate Ridge has found a reflective surface, thought to be the base of the gas hydrate zone, at 125 m beneath the sediment surface. This hydrate zone overlies a structure called Seismic Horizon A, along which methane-rich fluids appear to migrate from the underlying accretionary wedge. Bubble plumes are extremely visible here, and have not been shown to fluctuate with tidal cycles, as is the case on the Northern Hydrate Ridge. Instead, the rate of bubbling appears to follow a cycle unrelated to the tides. It has been suggested that this might be caused by the formation of gas hydrate seals close to the surface, which remain in place until the amount of gas accumulated in the sediment beneath them overcomes their resistance, then reform when gas emissions tail off sufficiently, a cycle which can take several years to complete. More recent surveys have established that while bubbling is not constant on the Southern Hydrate Ridge, it does appear to occur consitently at the same sites on the ridge, and can vary on an hourly timescale. This unexpected behaviour has led to a need for a more organised long-term monitoring of this system in order to understand it.

The systematic monitoring of activity has been carried out at several cold seeps, including a study on Clayoquot Slope, off the coast of Canada on the northern Cascadia Subduction Zone which lasted over a year, although the equipment used in that study was only able detect gas emissions when bottom currents were flowing in certain directions, hampering understanding of the system.

In a paper published in the journal Geochemistry, Geophysics, Geosystems on 21 September 2021, Yann Marcon of the Center for Marine Environmental Sciences and Department of Geosciences at the University of Bremen, Deborah Kelley of the School of Oceanography at the University of Washington, Blair Thornton of the Centre for In Situ and Remote Intelligent Sensing at the University of Southampton, and the Institute of Industrial Science at the University of Tokyo, and Gerhard Bohrmann, also of the Center for Marine Environmental Sciences and Department of Geosciences at the University of Bremen, present the results of a project that carried out systematic monitoring of the Southern Hydrate Ridge between July and November 2018.

Marcon et al. monitored gas emissions on the Southern Hydrate Ridge with the Southern Hydrate Ridge Rotating Sonar, which consists of a multibeam echosounder mounted on a rotator, with a rotating range of 360°. In addition they used a single-beam scanning-sonar connected to the Ocean Observatories Initiative's Regional Cabled Array to provide a finer detail monitoring gas releases at Einstein’s Grotto, one of the methane vents on the Southern Hydrate Ridge, and photo cameras also connected to the Regional Cabled Array to provide visual ground-truthing information about the dynamics and strength of bubble release, at Einstein’s Grotto and the Summit-A vent area. 

 

Top left: Location of Southern Hydrate Ridge. Top right: Map of the primary infrastructure of the Ocean Observatories Initiative's Regional Cabled Array observatory. Bottom: Overview map of the Southern Hydrate Ridge summit with the location of the Southern Hydrate Ridge Regional Cabled Array fibre optic cables, junction boxes and monitoring instruments. Shaded areas show the location of the main known vents. Marcon et al. (2021).

The bathymetry (depth of water) of the area was established in 2008 by the Autonomous Underwater Vehicle Sentry, operating from the Research Vessel Thomas G. Thompson, during preparation for the laying of the Ocean Observatories Initiative's Regional Cabled Array. A 3D photomosaic of the area was developed from imagery gathered by the University of Tokyo's Autonomous Underwater Vehicle AE2000f during the Schmidt Ocean Institute's FK180731 #Adaptive Robotics expedition.

A conductivity, temperature, and pressure (CTP) probe equipped with a dissolved oxygen optode sensor was used to monitor the conductivity, temperature, pressure, and dissolved oxygen concentration of the bottom water at one minute intervals. High-frequency tidal seafloor pressure was recorded with a tsunami pressure sensor. Current velocities were monitored with an upward-looking acoustic Doppler current profiler. Seismic data was collected by three ocean-bottom seismometers connected to the Regional Cabled Array. Wave height data was obtained from the National Data Buoy Center of the National Oceanographic and Atmospheric Administration.

Seafloor pressure at the Southern Hydrate Ridge was found to vary considerably with the tide, and was sensitive to the neep/spring tide cycle, with pressure varying by 1.4 dbar during neap tides and up to 3.8 dbar during spring tides. The seafloor temperature varied between 3.8°C and 4.5°C over the course of the study (June-November 2018) and between 3.7°C and 4.7°C over the longer period June 2018-June 2020, showing no long-term warming or cooling trend. Seafloor salinity varied between 34.26 to 34.37 psu over the period June-November 2018, while dissolved oxygen varied between 0.24 and 0.30 ml/L.

The Southern Hydrate Ridge Rotating Sonar carried out scans every two hours during the four month period of the experiment (with some gaps due to technical problems), producing a total of 888 readings. Of these, 886 (99.8%) detected gas bubbles, suggesting that bubbling was more-or-less constant. However, the amount of bubbling varied continuously, with peaks and troughs on a twice daily basis. These peaks and troughs appear to become larger at the spring tides and weaker at the neap tides, although the short duration of the experiment combined with the gaps in the data make it difficult to be completely confident about this.

Bubbling appears to be possible at any recorded pressure on the Southern Hydrate Ridge, although it was more pronounced when the pressure was low or falling. Two thirds of all peaks in activity occurred at times when the pressure was below average. The majority (65-70%) of the remaining third of peaks happened when the tide was decreasing, or changing (18-20%), with only a small proportion (15%) occurring while the tide was rising. However, there were some anomalies with this, most notably a large bubble release in July 2018m which occurred during a rising tide when the water pressure was above average.

 

Temporal variations of the Southern Hydrate Ridge Rotating Sonar backscatter magnitude and bottom pressure between 6 and 22 July 2018 (top plots) and between 19 October and 8 November 2018 (bottom plots). The backscatter magnitude non-linearly reflects the strength of the gas bubble emissions. The bottom pressure plot shows the local mixed tidal regime with diurnal and semi-diurnal constituents, as well as the fortnightly neap/spring tidal cycles. Bubble release is commonly stronger during ebb tide, and possibly also during spring tidal phases. However, some ebullition events do not correlate with the tide and may be triggered by local accumulation of pressurized free gas in the subsurface; the prominent peak observed on 18 July 2018 corresponded to the reactivation of the Summit-A vent after a very short venting interruption of about 4 hours; it did not affect the other vents at the Southern Hydrate Ridge summit and happened during flood tide within a neap tidal phase, hinting at shallow, local changes in the sediments. Marcon et al. (2021).

Eight different centres of bubbling were identified on the Southern Hydrate Ridge, with an average of four active at any given time. Five main clusters of activity were identified; each of these being 10-30 m across, and capable of producing more than one stream of bubbles at a time. These were named Smokey Tavern, Einstein's Grotto, Summit-A, Summit-B, and Summit-C. Bubbling at all of these sites was frequent, but not continuous, with sites remaining dormant for days at a time and all sites being active at the same time being a rare occurrence. As well as these main sites of activity around the summit of the Southern Hydrate Ridge, Marcon et al. detected at least six smaller venting sites, further away from the summit and much less active, which they named Smokey Tavern West, Summit-D, Far NE, Far S, Summit South, and Summit SW. Unlike the main sites, these sites were only sporadically active, and would often remain dormant for months between bouts of venting.

 

(a) Location of flare base points recorded with the Southern Hydrate Ridge Rotating Sonar between 8 July and 8 November 2018; the base points are grouped into clusters marking the location of the different Southern Hydrate Ridge vent sites. (b) Location of the main and periphery vents overlain on the photomosaic; the main vent sites are all located on areas covered with microbial mats. (c) Close-up view of the Southern Hydrate Ridge Rotating Sonar location and the Summit-A vent, with the 3D photomosaic in the background; a depression on the seafloor from Ocean Drilling Program drill site 1949 (ODP Leg 204) can be seen in the top-left corner as well as in the bathymetric data. (d) Close-up view of the 3D photomosaic at the Smokey Tavern vent showing the distribution of the microbial mats and the domed, collapsed and hummocky areas. Marcon et al. (2021).

The seafloor around the main vents is highly uneven, and covered by white microbial mats. These areas have numerous up-domed mounds, which extend laterally by as much as 35 m, with hummocky, jagged-edged depressions eaten into them, which are probably caused by the more-or-less constant venting of gas from these areas. The venting of gas does appear to be strongly tied to these areas, with venting restricted to them at all sites except Smokey Tavern, where it occurs across the entire microbial mat-covered dome structure. In the peripheral venting area this kink appears to be broken, with dark sediments and white areas of microbial matting visible, but venting not connected to these.

The sites closest to directly underneath the Southern Hydrate Ridge Rotating Sonar (Summit A and Summit B) appeared to be the most active, with sites moving away from this area being progressively less active. This might indicate that the sonar was better act detecting gas emissions directly beneath it and less good at detecting them further away. Alternatively, it might be a reflection the fact that the sonar was placed directly over the highest point of the Southern Hydrate Ridge, so that the most active points were those in the shallowest water, with sites becoming progressively less active as the water grows deeper.

None of the vents was active all the time, although venting over the wider Southern Hydrate Ridge area was continuous. During the period 6-22 July 2018, The Summit A vent was active 75% of the time, Einstein's Grotto was active 69% of the time, Smokey Tavern was active 65% of the time, Summit B and Summit C were active 54% of the time, Summit D 22% of the time, Far NE 9%, Far S 2%, and Smokey Tavern West was active 1% of the time, while Summit South and Summit SW were completely inactive. During the period 19 October-8 November 2018, the Smokey Tavern vent was active 44% of the time, Summit B 30% of the time, Summit C 70%, Summit D 23%, and Smokey Tavern West was active 6% of the time. A sudden decrease in activity at one site was usually accompanied by an equally sudden increase at another. For example, a pause in venting at Summit A on 10 July 2018 was marked by a sudden increase at Summit C. On 12 July activity at Summit C fell off again, and activity resumed at Summit A and Summit B. During the period 19 October-8 November 2018, Summit B was only active when Summit C was inactive, and vice versa. These synchronous changes in activity were frequent enough that they are unlikely to be coincident. Their timing also appears to be linked to the daily tide cycles. 

Southern Hydrate Ridge Rotating Sonar magnitude data from 19 October to 8 November 2018 for individual plume clusters. Einstein's Grotto and Summit-A are not shown because of the restricted 245° scanning sector of the Southern Hydrate Ridge Rotating Sonar after 10 October 2018. Far NE, Far S, Summit South, and Summit SW are not shown because they were inactive over this period. The vertical axis is logarithmic to facilitate visualisation of low magnitude variations. Absolute magnitude values cannot be compared between the clusters due to a distance bias and are not shown. Marcon et al. (2021).

A closer examination three vents at Einstein's Grotto over a 24 hour period found that, while they were all bubbling continuously throughout the day, the amount of outflow from them varied considerably over the day, with the bubbles undergoing sudden peaks in activity, followed by slower tailing off, several times per day. Furthermore, these peaks in activity always occured when the tide was high or waning.

Cameras directed at the Summit A and Einstein's Grotto vents were able to confirm that the events detected by sonar were in fact bubble releases. The one directed at Einstein's Grotto further revealed that the depression from which the bubbles were escaping was growing slightly wider with each bubble-release event, probably due to the loss of gas hydrates within the sediment, and that during major bubble releases this was accompanied by slumping of the walls of the depression and the collapse of overhanging sections. In some cases, hydrates were exposed by sediment loss, and then rapidly lost. Currents on the seafloor also appeared to contribute to the rate of erosion, by slowly breaking up blocks of sediment. The video films also revealed that events recorded as coming from a single vent could in fact come from different locations within the vent at different times, and that sometimes the location of bubble releases shifted in response to sediment movements. On occasions bubbles were seen emerging from as many as four different locations within a vent.

It was only possible to measure the velocity of bubble streams when they were visible to a camera and immediately adjacent to a measuring scale, but those that could be measured rose at speeds of between 18 and 34 cm per second, with an average speed of 25 cm per second.

The camera directed at the Einstein's Grotto vent detected a significant gas blowout between 0.46 and 1.16 am on 23 July 2018, with a sudden release of a significant volume of gas, along with ejected sediment, which led to a change in the seafloor topography. The event happened about midway through a rising tide, with gas release being week, but active, both before and after the event. 

 

A pressure outburst was documented by the CAMDSB103 camera on 23 July 2018. The camera images show sediment resuspension shortly (0–30 min) after the outburst. Images taken after visibility improved show significant seabed changes including the presence of a large well-lithified sediment block into the collapsed area subsequent to the blow out. Scanning-sonar scans recorded before and after the event show that the seabed morphology at the location of the outburst changed over an area of at least 3 m². The hummocky area east of the sonar is part of the Einstein's Grotto vent. The range of the sonar scans is 20 m. The laser pointers on the camera images are 10 cm apart. In the difference plot, blue and red colours show negative and positive differences respectively. Marcon et al. (2021).

Turbulence in the upper part of the water column was relatively high throughout the study, with currents having an average velocity of 50 cm per second. The depth of this layer varied with season and time of day, between about 300 and about 400 m. Below this the water was much calmer, with velocities below 15 m per second, although here too there were daily and seasonal variations. Currents on the seafloor generally run from the northwest. Upwelling was also a significant component of bottom currents, with upwelling currents of up to 5 cm per second rising for about 300 m (i.e. to a depth of 470 m), where they generally became undetectable, although some reached as high as 400-350 m below the surface, by which time they had lost much of their initial velocity. These upwelling flows were intermittent, generally appearing when the prevailing northwest current was either weak or reversed, and appeared to be linked to episodes of bubbling, although this could be an indicator that the northwest current was deflecting bubbles away from the sonar beam.

Contrary to expectations, no connection was found between bubble outbursts and seismic events. A number of such events were measured during the study period, none of which were linked to conspicuous changes in bubble activity.

Wave height was found to be strongly seasonal in the study area, with the monthly average wave height between October and April exceeding 3 m and individual waves reaching close to 10 m, whereas between May and September the monthly average remained below 2 m, and the highest recorded waves little over 3 m. No correlation was found between wave height and bubble activity.

Macron et al.'s study shows that the Southern Hydrate Ridge has a number of vents (where 'vent' is defined as 'a distinct area of the seafloor where gas ebullition recurs') and that each vent has a number of bubble outlets, with vents capable of producing bubbles from several bubble outlets at once, often at different rates of activity.

Five main vents, and six peripheral vents were detected, a significant increase on the number found by previous, ship-based surveys, although it is possible that others exist and were missed by the study. Macron et al. note that bubble events have been recorded at two other sites on the Southern Hydrate Ridge (named Central and Pinnacle), that were outside the scope of their survey.

The discovery that there are multiple bubble-producing sites within each vent, which may be active at different times and at different rates at the same time, is new. This potentially presents additional challenges for ship-based surveys, as snapshots of bubbling from different locations might not be recognised as the same vent, particularly if the origin of bubbles is further complicated by varying currents.

The main vents all appear to be up-domed and hummocky areas covered by microbial mats. Such areas have previously been linked to the presence of gas hydrates at shallow depths within the sediment, something which was confirmed by Macron et al.'s study. The hummocky topography seen at these locations appears to be directly linked to bubble-venting, which causes changes the seafloor morphology quite rapidly at vent sites.

The loss of gas hydrate deposits is likely to be largely due to direct disolution of gas into non-methane saturated water, without the formation of bubbles. The vent zone of the Southern Hydrate Ridge lies within the gas hydrate stability zone (approximately between 500 and 900 m below sea level), so the excess loss of gas hydrates through bubble formation is unlikely in shallow sediments here. The depressions and hummocky surfaces observed at the site could as easily be formed by hydrate dissolution as by bubble formation, particularly at a site being regularly scoured by currents of non-methane saturated water. Based upon this, Macron et al. suggest that the bubbles observed venting on the Southern Hydrate Ridge are not being formed by the disassociation of gas hydrates, but rather are bubbles of trapped within the sedimenr that are released into the water.

Previous studies of the Southern Hydrate Ridge have captured only snapshots of bubbling activity there, suggesting that bubbling was either 'off' or 'on' at different times. This is consistent with the idea that methane was being delivered to the system from a reservoir more deeply buried gas at Horizon A, which was escaping intermittently through a system of cracks in the overlying rock. Macron et al.'s study contradicts this model, showing that bubbling is more-or-less constant on the Southern Hydrate Ridge, although different parts of the system are active at different times, and that this activity is strongly linked to bottom pressure, and thereby to the tides. However, Macron et al. cannot rule out the possibility that the vents are connected in some way, or that there may be some form of interaction between them.

Tidal modulation of methane vent systems on accretionary wedges has previously been suggested, but until now there has not been sufficient evidence to support this. Notably, video evidence from the Northern Hydrate Ridge appeared to show a correlation, but was not sufficient on its own to prove the link. Therefore the long-term sonar study carried out by Macron et al. at the Southern Hydrate Ridge clearly establishes a relationship between tides and bubbling for the first time. A relationship has also been suggested between tides and bubbling at cold seep sites, which appears to have been supported by observations off the coast of Canada.

Macron et al. suggest that this link is related to the effect that pressure has upon pore spaces within sediments, which are pushed shut at higher pressures (i.e. when the tide is high) and pulled open at lower pressures, allowing gas bubbles trapped within the sediment (where the water is methane-saturated) to escape. At spring tides, the pressure loading on the seafloor would be higher than at neep tides, causing the dilation of pore-spaces deeper into the sediments, which would in turn result in more bubbles being released, something line with Macron et al.'s observations. 

However, this does not appear to be the only factor at play; Macron et al.'s theory can explain why vents tail of activity after outbursts, when they might be expected to have reduced numbers of bubbles within their sediments, but not what causes the reactivation of individual vents after periods of inactivity. Furthermore, a number of significant bubble outbursts were recorded at times which appeared to show no connection to tidal cycles. Another problem with this hypothesis is the absence of any connection with seismic activity. Earthquakes would be expected to cause changes in pore spaces, which should have resulted in bubble releases, but despite several Earthquakes being recorded during the study period, none of them was linked to any change in bubble-activity.

One possibility previously suggested is that gas hydrates accumulating in pore spaces trap a layer of gas below the surface sediments, in Horizon A, which is released when the gas pressure builds up to a point where it overcomes the resilience of the hydrates. This would explain how vents become dormant and then reactivate after a period of inactivity, but the time scale predicted for this model does not fit Macron et al.'s data. Under this model the vents should be inactive for years at a time, whereas the observed quiet periods lasted from a few hours to a few months. Macron et al. suggest that possibly the basic premise of this hypothesis is correct, but that the gas is being trapped much closer to the surface by a less substantial hydrate lid, enabling smaller, more frequent bubble-outbursts from beneath a lid more easily overcome.

This would allow bubble release to be controlled at a local level, will small pockets of trapped gas building up within sediments in the gas hydrate solubility zone, beneath shallow blockages in the sediment pore-system. Overcoming these shallow blockages would require much less pressure to build up, with the increased pressure from tidal forces often being sufficient to trigger outbursts. 

The perpheral sites, where venting occurs but is far less frequent, may be receiving lower levels of gas from the underlying feeder sediments, or may be acting as pressure-release valves for a larger gas system beneath the gas hydrate solubility zone, venting less frequently as is predicted by the deep-reserve, large hydrate-lid model. 

The strong bottom currents observed at the Southern Hydrate Ridge also ought to play a role in the gas hydrate dissolution cycle, since these currents constantly bring in new water unsaturated in methane, leading to more rapid hydrate dissolution. 

Macron et al. note that strong upwelling currents are often observed at the Southern Hydrate Ridge, and that these tend to coincide with outbursts of bubble activity. They suggest that the upwelling currents may in fact be driven by the gas bubbles dragging water along with them as they rise. Curiously, however, the upwelling component of the system appears to be more strongly tied to the tidal system than the bubble activity is, with upwellings tending to stop during rising tides, while bubble activity frequently continues. Both upwelling currents and bubbles appear to reach depths slightly above the gas hydrate stability zone, which is consistent with the two phenomena being linked and the bubbles being protected by a hydrate-skin. The height to which both bubbles and upwelling currents rise varies seasonally, which is likely to be linked to seasonal water stratification.

Methane bubbling from the Southern Hydrate Ridge is a more-or-less constant phenomenon, although the location of the bubbling does vary over time. A number of vents are present, with the controls on bubbling at each of these apparently being independent. The continuous venting of bubbles appears is linked to the slow erosion of sedimentary structures on the seafloor, with occasional more substantial outbursts provoking more substantial overturn. The timing of bubble venting appears to be linked to tidal cycles, and is probably driven by hydrostatic pressure, although some bubble releases appear to be random and unconnected to tidal cycles.

Bubbling is more prevalent at low and falling tides, when pressure is low or falling, and this is more notable around spring tides, when pressure changes are more marked. At these times pore spaces in the sediment are more open, which could conceivably be related to outbursts of bubbling. However, bubbling also occurs at other times, which may indicate that pressure within the sediment is also a significant influencing factor. 

The main vents on the Southern Hydrate Ridge were active for between 50 and 75% of the time, although the level of activity at 'active' vents varied considerably in intensity, and could come from multiple locations within the vents. This makes it hard to estimate the amount of methane being released by the Southern Hydrate Ridge, and Macron et al. were unable to estimate this, despite having undertaken the most detailed study of the system to date. Based upon their findings they do not feel it would be reasonable to extrapolate data from a single vent across the whole system, instead any attempt to estimate the amount of methane being released would require long-term monitoring of the entire system. 

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Manayunkia occidentalis: A new species of Sabellid Polychaete from the Pacific Northwest of the United States, and an alternate host of two Myxosporean parasites of Salmonid Fish.

Annelids are a diverse and speciose invertebrate group, particularly in marine systems. Apart from Clitellate Annelids ('Oligochaetes' and 'Leaches'), there are relatively few known freshwater species, and several of these belong to the Sabellid genus Manayunkia. Manayunkia currently contains 11 accepted nominal species, though this may need further assessment. The most recent taxa described are the marine Manayunkia mizu, described in 1996 from Papua New Guinea, and the freshwater Manayunkia zenkewitschii, described in 1997 from Lake Baikal. Currently, there are freshwater Manayunkia described from Europe and North America, and brackish/marine species known from Australia, Europe, Papua New Guinea and Brazil. Two species of Manayunkia are recorded from North America: Manayunkia aestuarina, from brackish coastal environments (though the type locality is in the UK), and Manayunkia speciosa, which was first briefly described by Joseph Leidy in 1859, from the Schuylkill River in Pennsylvania, and in much greater detail from specimens from New Jersey in 1883. The species was later reported from the Great Lakes in 1829, the Klamath and Sacramento river basins of Oregon and California in 1966, lakes in Alsaka in 1967, and lakes in North Carolina in 1971. Manayunkia speciosa has been identified as the invertebrate alternate host of two Myxosporean parasites of Salmonid Fish: Ceratonova shasta (formerly Ceratomyxa shasta) and Parvicapsula minibicornis. Myxosporeans are common Myxozoan Cnidarian parasites with complex life cycles that require two hosts: a vertebrate (usually a Fish) in which parasite Myxospores develop, and an invertebrate (usually an Annelid) in which actinospores develop. Both Ceratonova shasta and Parvicapsula minibicornis are widespread in the Pacific Northwest but have not been recorded from the Great Lakes, or east coast of North America, despite presence of both Manayunkia speciosa and susceptible Salmon hosts in these regions.

In a paper published in the journal Zootaxa on 17 March 2020, Stephen Atkinson and Jerri Bartholomew of the Department of Microbiology at Oregon State University, and Greg Rouse of the Scripps Institution of Oceanography at the University of California, San Diego, present the results of a survey based upon the hypothesis that that these two Myxozoans actually require a heretofore unrecognized Annelid host, which is present only in western North American river basins, and which has been consistently mis-identified as Manayunkia speciosa.

Atkinson et al. sampled both infected and uninfected Annelids from the two localities where the parasites were recorded originally from their annelid hosts: the Klamath River, California, and the Willamette River, near Corvallis, Oregon. Using morphology and mitochondrial Cytochrome oxidase subunit I DNA sequencing, they compared these specimens with Manayunkia speciosa samples from New Jersey and the Great Lakes. Atkinson et al. discovered that all Klamath and Willamette Manayunkia, both infected and uninfected, were a novel species, they further sequenced Annelid samples from collections made between 2006 and 2018 and identified only the new species. They did not detect any Manayunkia speciosa from either river basin.

Annelids were collected by hand at depths of 10–50 cm from rocks and periphyton from the Klamath River, California, from below Iron Gate Dam. Additional specimens were collected from the Willamette River, Oregon. Under a dissection microscope, living Annelids were separated from substrate, then examined by light microscopy either alive or fixed in 10% neutral buffered formalin, frozen for DNA analysis, or fixed in 2% glutaraldehyde in cacodylate buffer for electron microscopy. Type and voucher specimens were deposited in the Benthic Invertebrate Collection at Scripps institution of Oceanography, La Jolla, California. To confirm identity and infection status, Atkinson et al. examined additional archived Annelid samples collected opportunistically 2006–2018 by Oregon State University as part of their long term, on-going ecological and disease studies of parasites Ceratonova shasta and Parvicapsula minibicornis. These samples were collected from localities in the Klamath and Willamette Rivers. Atkinson et al. also obtained Manayunkia speciosa from Lake Superior (St. Marys River, Ontario, Canada) and South River, New Jersey, in 2009. A marine Fabriciid, Echinofabricia goodhartzorum, was used as the outgroup, since Echinofabricia has been shown to be the sister group to Manayunkia.

Live Annelids were found in clusters of tubes, most often attached to rocks or intertwined with periphyton. Females were observed frequently with broods of larvae in their tubes. Males and females with overt parasite infections often lacked gametes. Five individuals were sequenced from the type collection locality/date, with an additional 79 from archival material from the Klamath River; 10 were sequenced from the Willamette River. The five paratype specimens were up to 1.6% divergent with each other (0–6 nucleotides differed over the total alignment of 439 nucleotides), compared with a divergence of up to 2.8% among all 84 Klamath River Annelids sequenced. The 10 Willamette River specimens were up to 0.4% divergent with each other, and pairwise distances between Willamette and Klamath River specimens were 3.1–4.1%. These west coast samples were 10.5%–12.2% divergent from the Great Lakes and East Coast Manayunkia speciosa reference sequences. The parasite Ceratonova shasta was detected in 16 Annelids from the Klamath River, whereas Parvicapsula minibicornis was detected in four annelids from the Klamath River and one from the Willamette River; these parasite abundances were typical.

The new species is named Manayunkia occidentalis, which is derived from the Latin word for 'west', to contrast with Manayunkia speciosa, which occurs in eastern and central North American drainages. The holotype (SIO-BIC A12115) is a male with eight thoracic segments and three abdominal segments. Total length (unfixed) 3.0 mm, crown 0.3 mm. Body cylindrical with tapering, dorso-ventrally flattened abdomen. Body wall translucent grey with minor brown pigmentation on peristomium and pygidium, and green pigmentation on chaetiger 6. Branchial crown about 10% of total body length. Two pairs of radioles, each with six pinnules. One ventral pinnule on radiole with 4–5 yellow-white spots in life. One pair of vascularised, unbranched ventral filamentous appendages present, extending for about two-thirds length of radiolar crown, approximately same width as pinnules. Anterior peristomial ring with membranous collar, followed by posterior peristomial ring. Collar margin smooth, higher ventrally, separated by a narrow dorsal gap that corresponds with ciliated faecal groove. Peristomial eyes, black rounded spots. Pygidial eyes absent. Superior thoracic notochaetae elongate, narrowly hooded; 5–7 per fascicle (chaetigers 1–5), 4–5 per fascicle (chaetigers 6–8). Inferior thoracic notochaetae on chaetigers 1–8 short; 3–4 per fascicle except chaetiger 2, which has 6 per fascicle. Thoracic neuropodia each with 4–7 uncini in chaetigers 2–8. Thoracic uncini with rows of evenly small teeth gradually decreasing in size away from main fang. Position of chaetae and uncini reversed in abdominal segments; number of abdominal uncini per fascicle decreasing posteriorly from 22 to 9. Abdominal uncini each with multiple rows of teeth that are uniform in size; manubrium at least five times longer than dentate region, with base about two thirds the width of the dentate region. Abdominal neuropodia are elongate, narrowly hooded, decreasing posteriorly from 4–6 to 2 per fascicle.

 

Gross morphological features of Manayunkia occidentalis resolved by light microscopy: (A) multiple individuals emerged and feeding from their tubes; (B) Individual annelid with prominent vascularized appendages (va) and showing refractile spots on one feeding palp on each side (arrowheads); (C) female in reflected light, showing white oocytes (o) in segments 4–6; (D) male in reflected light showing bright spermatogonic tissue (sp) in multiple posterior segments; (E) Male in transmitted light showing parallel vascularized appendages (va) and fanned-out feeding palps nteriorly with two dark eyespots in peristomium, and granular coelom posteriorly due to presence of developing sperm. Atkinson et al. (2020).

Paratypes are similar to the holotype. However, females have oocytes in thoracic chaetigers 4–5 and a pair of pigmented spermathecae in the base of the radiolar crown. Females differ from males in having thoracic neuropodia with uncini in chaetigers 2–5 followed by 3–6 elongate hooded chaetae in neuropodia of chaetigers 6–8. 

 

Images showing chaetal characters of Manayunkia occidentalis: (A) inferior and superior notochaete typical of thoracic segments 2–8; (B) thoracic uncini; (C) abdominal uncini; (D) dorsal view of posterior thoracic segments and abdomen of male showing typical uncini in chaetigers t7 and t8 (arrowheads) and in scanning electron micrograph shown in (F); (E) dorsal view of posterior thoracic segments and abdomen of female showing neuropodia of thoracic chaetigers 6–8 with elongate neuropodia instead of uncini, seen also in scanning electron micrograph in (G) (arrowhead). (H) anterior thoracic segment of female showing notochaetae and uncini (arrowhead), characteristic of thoracic segments 2–5 in both sexes. Atkinson et al. (2020).

Manayunkia speciosa was described originally from Philadelphia, USA with subsequent reports from the Great Lakes and several west coast river basins. This Annelid is reported to be the obligate alternate host of two Myxozoan parasites Ceratonova shasta and Parvicapsula minibicornis. Unambiguous identification of the invertebrate hosts of Myxozoans, which produce the infectious stage to Fish, is essential for risk assessment and stock management as these parasites cause disease and death within populations of salmon and trout. Atkinson et al.'s findings support the hypothesis that the Annelid host of the parasites has likely been mis-identified as Manayunkia speciosa, and is actually a novel taxon Manayunkia occidentalis.

 

Morphological features of Manayunkia occidentalis resolved by scanning electron microscopy: (A) lateral view; (B) dorsal view; (C) ventral view; (D) anterior showing membranous collar (c) of the peristomal ring (pr), margin with fecal groove (fg); mucus covers the pinnules and adheres Diatoms; (E) detail of typical thoracic uncini; (F) abdominal segments and anus, showing ciliated fecal groove extending anteriorly and wrapping around to the ventral surface at boundary between abdominal and thoracic segments; (G) lateral view of thoracic segments showing contracted uncini and prominent neuropodia; (H) higher magnification view of retracted abdominal uncini. Atkinson et al. (2020).

The 94 west coast Manayunkia occidentalis specimens that Atkinson et al. characterised had cytochrome oxidase subunit I sequences at least 11% different from the reference Manayunkia speciosa sequences from Lake Superior and New Jersey. This east-west genetic divergence underpinned the rationale for describing the west coast Annelids as a distinct, novel taxon. Among the Manayunkia occidentalis specimens, the greatest genetic difference (4.1%) was between isolates from the two rivers, which are more than 500 km apart. These genetic differences are not surprising given the relative immobility of the Annelids, particularly from above- and below-dam localities, and between river basins separated by saltwater. Atkinson et al. hypothesise that similar degrees of genetic differences, with corresponding novel haplotypes, will be observed among populations in other unconnected river basins on the West Coast (Fraser, Rogue, Sacramento), and probably within large basins like the Columbia.

Atkinson et al. did not detect any Manayunkia speciosa among the 94 Annelids sampled from multiple localities in two river basins. This was surprising given historical records of that taxon in West Coast basins, particularly associated with Myxozoan parasites. The collection localities in the Klamath River included one where 'Manayunkia speciosa' was collected and sequenced previously. This published sequence is only minimally divergent (0–1%) from Manayunkia speciosa reference sequences collected from Lake Superior and the East Coast. Atkinson et al. cannot explain how these trans-continental Manayunkia speciosa sequences could be so similar, given that they observed genetic distances up to 2.8% among Manayunkia occidentalis samples from the Klamath Basin, and up to 4.1% between specimens from different West Coast river basins. Based on their survey data, Atkinson et al. postulate that Manayunkia speciosa may not be present in the Klamath or Willamette rivers, and they suspect that the earlier assignations of Klamath River Annelids as Manayunkia speciosa are incorrect. Almost all previous identifications relied on morphology, and Atkinson et al. have now shown that there are few morphological characters to distinguish the two taxa, though the markedly smaller number of pinnules in Manayunkia occidentalis is an obvious difference from Manayunkia speciosa. This and the cytochrome oxidase subunit I sequence divergence of at least 10.5% makes future discrimination between Manayunkia speciosa and Manayunkia occidentalis relatively straightforward.

Twenty-one of the 94 examined annelids were infected with either or both Ceratonova shasta and Parvicapsula minibicornis, and all were identified by sequence as Manayunkia occidentalis, and thus Atkinson et al. could not confirm that Manayunkia speciosa is a host for these Myxozoans. If Manayunkia speciosa is not a permissive host, then this would explain why Ceratonova shasta and Parvicapsula minibicornis have not become established in the Great Lakes or in East Coast river systems where Manayunkia speciosa, only, is present. It is likely, however, that Manayunkia speciosa hosts other Myxozoan species, as evidenced by detection of Ceratonova-like DNA in Annelids from the Great Lakes. Atkinson et al. predict that they will find Manayunkia occidentalis in all river basins where the parasite is found on the west coast, and none in the Great Lakes. Accordingly, they are sampling and sequencing additional Annelid populations from river basins where Ceratonova shasta and Parvicapsula minibicornis occur, to determine the phylogeography of the host, any correlation between infection and host haplotype, and if any Manayunkia speciosa sensu stricto exists on the west coast of North America.

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Magnitude 4.5 Earthquake in Curry County, Oregon.

The United States Geological Survey recorded a Magnitude 4.5 Earthquake at a depth of 16.7 km, roughly 6 km to the northeast of the city of Port Oreford in Curry County, Oregon, at about 1.45 am local time (about 9.45 am GMT) on Saturday 30 November 2019. This was not a large quake, and no damage or injuries have been reported, but it was across much of southwest Oregon and in parts of northern California.

The approximate location of the 30 November 2019 Curry County Earthquake. USGS.

Oregon forms the southern part of the Cascadia Subduction Zone, along which the Juan De Fuca plate, which underlies part of the northeast Pacific, is being subducted beneath the western margin of the North American Plate. This is not a smooth process, and the two plates frequently stick together then break apart again as the pressure builds up, causing Earthquakes in the process. The heat and pressure within the Earth also slowly melts the subducting plate, liquefying more volatile minerals which then rise through the overlying North American Plate as magma, fuelling the volcanoes of America's Pacific Northwest.

Subduction along the Cascadia Subduction Zone. Kathleen Cantner/American Geosciences Institute/Earth Magazine.

Witness accounts of quakes can help geologists to understand these events and the rock structures that cause them. If you felt this quake (or if you were in the area but did not, which is also useful information) you can report it to the United States Geological Survey here.

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Looking for a connection between the Columbia River Flood Basalts and the Middle Miocene Climate Optimum.

Flood basalts are large volumes of basalt erupted from deep mantle plumes, which cover large areas of land with volcanic basalt rock in a relatively short time, geologically speaking (hundreds of thousands to millions of years). Like other volcanic eruptions they also release climate altering carbon dioxide and sulphur dioxide gasses, and do so in very large volumes. This is thought to have a very profound effect on the climate, and flood basalts are often closely linked to mass extinction events, for example the Siberian Traps Flood Basalt is associated with the End Permian Extinction, the Mid-Atlantic Flood Basalt with the End Triassic Extinction, and the Deccan Traps Flood Basalt with the End Cretaceous Extinction. The youngest known flood basalt is also the youngest; the Columbia River Flood Basalt, in the Pacific Northwest of the United States, erupted between 17 and 5 million years ago, from a north-south trending fissure system than covered parts of eastern Washington, eastern Oregon, western Idaho, and northern Nevada. This is coincident with a wider outbreak of volcanism in the area, associated with the subduction on the Cascade Arc, which fuelled volcanism in central Oregon and northern Nevada, and the Yellowstone–Snake River Plain Hotspot, which fuelled volcanism in western Idaho and eastern Wyoming. For this reason, plus difficulties constraining the dates of the basalt eruptions, the Columbia River system is not universally accepted as a true-mantle-plume-driven flood basalt. Nor is the Columbia River Flood Basalt associated with an extinction event, though its onset does appear to be correlated with the Middle Miocene Climate Optimum, 16.5 million years ago, a period of rapid warming associated with a spike in atmospheric carbon dioxide, that saw the retreat of the Polar Ice Caps, and major climatic perturbations in many areas.

In a paper published in the journal Science Advances on 19 September 2018, Jennifer Kasbohm and Blair Schoene of the Department of Geosciences at Princeton University publish a new chronological sequence for the Columbia River Flood Basalts, based upon Uranium-Lead Zircon dating.

Zircons are volcanic minerals that form within molten rock as it cools. Like other such minerals, zircons will incorporate some elements present in the melt, but not others, notably they will incorporate uranium, but not lead. This is important because uranium is an unstable element, and over time undergoes fission, with the uranium atoms breaking down to produce, amongst other things, lead atoms. This is very useful because nuclear fission occurs at a steady rate, unaffected by conditions such as temperature or pressure, so that by comparing the proportion of uranium to lead within a zircon crystal.

One problem with this is the remarkable stability of zircon crystals. Zircons form in cooling magma and volcanic melts where the right elements are present, but unlike other such minerals can survive being reheated past the temperature at which they originally formed. This enables zircons to survive the melting of rock along subductive plate margins, and subsequent re-eruption through volcanoes along these margins. The durability of zircons has proved extremely useful to scientists studying the early evolution of the Earth, as the oldest minerals on the planet are zircons far older than their host rocks, but is a serious problem in an area like the Columbia River Flood Basalts, where material from a deep mantle plume has erupted through recent volcanic rocks associated with a subductive plate margin, where most of the material being subducted was older volcanic rock, something that has made it very hard to date the Columbia River sequence.

In order to resolve this problem Kasbohm and Schoene took samples from eight horizons within the Colombia River Sequence, then tested a large number of zircons (20-40) from each sample, selecting the youngest age present in each sample to represent that part of the sequence. Using this method, they were able establish that the upper 72% of the Steens Basalt, the oldest rocks of the sequence, erupted between 16 653 000 and 16 589 000 years ago, the overlying Imnaha Basalt erupted around 16 572 000 years ago, the Grande Ronde Basalt, which overlies the Imnaha Basalt, finished erupting around 16 066 000 years ago, and the lowest 77% of the Wanapum Basalt, close to the top of the sequence, had erupted by 15 895 000 years ago.

Map of Columbia River Flood Basalts and regional volcanism. The map shows the areal extent of each formation of the Columbia River Flood Basalts, and the legend provides the volume contribution of each formation. Stars represent geochronology sample collection sites; dashed lines enclose areal extent of source dike swarms. The Prineville Basalt and Picture Gorge Basalt are coeval with the Grande Ronde Basalt, represent 1.4% of the total Columbia River Basalt volume, and are grouped with the Grande Ronde Basalt for all volume estimates presented here. Kasbohm & Schoene (2018).

This implies that 95% of the total volume of the Columbia River Flood Basalts erupted within 758 000 years, between 16 653 000 and 15 895 000 years ago. If correct, this means that the Columbia River Basalts were erupted at a remarkably high rate even for flood basalts, with peak rates of between 20 and 40 cubic kilometres of material per year being produced. This compares to estimates of peak eruption levels for the Deccan Traps Flood Basalts of between one and two cubic kilometres per year, for the Central Atlantic Flood Basalts of three to five cubic kilometres per year, and for the Siberian Traps Flood Basalts of between one and four cubic kilometres per year.

Such a large volume of volcanic material being erupted over such a short time would have had a very strong effect on the atmosphere, potentially doubling the amount of carbon dioxide in a relatively short period of time. This correlates well with the onset of the Middle Miocene Climate Optimum at 16.5 million years ago. The Middle Miocene Climate Optimum was followed my the Middle Miocene Disruption, which began around 14 million years ago, when falling carbon dioxide levels led to plunging temperatures, and an extinction event that removed many warm adapted groups from higher latitudes. This suggests that the rapid eruption of volcanic material created a spike in atmospheric carbon dioxide that lasted around a million years after the eruptions ceased.

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Fluminicola umpquaensis & Fluminicola fresti: Two new species of Pebblesnail from Oregon.

Pebblesnails, Fluminicola spp., are small globose to conical freshwater Snails found in the watersheds of western North America from California to British Colombia. The Snails inhabit a range of habitats from small seeps and springs to large rivers and lakes, with the group thought to contain many species, each with a limited range and specific habitat requirements. Despite this, only twenty-five species have been described to date, fourteen of which come from the Sacramento River Basin and six from the Columbia River Basin, with many other known populations that have historically been grouped into a small number of widespread populations, something which is now believed to be erroneous. Many populations of Pebblesnails are thought to be at risk due to Human activities, and gaining a proper understanding of their taxonomy is crucial before any legal protection for these species can be gained.

In a paper published in the journal ZooKeys on 8 June 2017, Robert Hershler of the Department of Invertebrate Zoology at the Smithsonian Institution, and Hsiu-Ping Liu and Niko Hubbart of the Department of Biology at the Metropolitan State University of Denver, describe two new species of Pebblesnails from the Umpqua and Rogue River Basins in Oregon.

Hershler et al. carried out gene sequencing and morphometric analysis of 161 Pebblesnails from 35 sites in the Umpqua and Rogue River basins. From this they were able to detect three distinct clades of Pebblesnails. One of these was identified as a new population of Fluminicola multifarius, a species previously known from the Sacramento and McCloud river basins in California. The distribution of this species is now extended to include the southern part of the upper Rogue River Basin. This also raises the possibility that the species might be found in the Klamath River Basin, which lies between the Sacramento and Rogue basins, and where the species has not yet been recorded. The remaining two populations are described as new species. 

Shells, opercula and radula, Fluminicola multifarius from the Rogue River Basin in Oregon. (A) Shell. (B) Shell. (C) Shell. (D), (E) Opercula (outer, inner sides). (F) Portion of radular ribbon. (G) Central teeth. (H) Lateral teeth. Scale bars: (A)–(B) 1.0 mm; (D)–(E) 250 μm; (F), 100 μm; (G)–(H) 10 μm. Hershler et al. (2017).

The first new species is named Fluminicola fresti in honour of the late Terrence Frest, for his contributions to the study of malacology in the northwestern United States. This species was found in spring-fed environments in the upper parts of both river basins, to the north of Little Butte Creek. The species is small to medium sized for the genus, reaching 2.3 to 5.5 mm in height, with a trochoidal to ovate-conic shell, 3.5-4 whorls when fully grown and an ovate aperture. 

Shells, opercula and radula, Fluminicola fresti. (A) Holotype. (B), (C) Sympatric ovate-conic and trochiform shell morphs, respectively. (D) Shell. (E), (F) Opercula (outer, inner sides). (G) Portion of radular ribbon. (H) Central teeth. (I) Lateral teeth. Scale bars: (A)–(D) 1.0 mm; (E)–(F) 250 μm; (G) 100 μm; (H)–(I) 20 μm. Hershler et al. (2017).

The second new species is named Fluminicola umpquaensis, meaning ‘from Umpqua’, the species being widely distributed in the Umpqua River Basin but not known from elsewhere. The species is large for the genus, reaching 9.5 mm in height, with a conical and a spire that tends to erode, leaving it with somewhere over 3.5 whorls when mature. The species was found in springs, streams and rivers in the Umpqua Basin.

Shells, opercula and radula, Fluminicola umpquaensis. (A) Holotype. (B) Shell. (C) Shell. (D), (E) Opercula (outer, inner sides). (F) Portion of radular ribbon. (G) Central teeth. (H) Lateral teeth. Scale bars: (A)–(E), 1.0 mm; (F), 100 μm; (G)–(H), 10 μm. Hershler et al. (2017). 

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