Author Archive for mmaheigan – Page 25

Shipboard LiDAR: A powerful tool for measuring the distribution and composition of particles in the ocean

Posted by mmaheigan 
· Tuesday, October 23rd, 2018 

Despite major advances in ocean observing capabilities, characterizing the vertical distribution of materials in the ocean with high spatial resolution remains challenging. Light Detection and Ranging (LiDAR), a technique that relies on measurement of the “time-of-flight” of a backscattered laser pulse to determine the range to a scattering object, could potentially fill this critical gap in our sampling capabilities by providing remote estimates of the vertical distribution of optical properties and suspended particles in the ocean.

A recent article in Remote Sensing of Environment details the development of a portable shipboard LiDAR and its capabilities for extending high-frequency measurements of scattering particles into the vertical dimension. The authors deployed the experimental system (shown in Figure 1a) during research cruises off the coast of Virginia and during a passenger ferry crossing of the Gulf of Maine (associated with the Gulf of Maine North Atlantic Time Series program-GNATS). Remote measurements of LiDAR signal attenuation corresponded well with simultaneous in situ measurements of water column optical properties and proxies for the concentration of suspended particles. Interestingly, the researchers also observed that the extent to which the return signal was depolarized (also known as the LiDAR depolarization ratio) may provide information regarding the composition of particles within the scattering volume. This is evidenced by the strong relationship between the depolarization ratio and the backscattering ratio, an indicator of the bulk composition (mineral vs. organic) of the particles within a scattering medium (Figure 1b).

Figure 1. a) LiDAR system deployed to look through a chock at the bow of the M/V Nova Star. b) Relationship between the LiDAR linear depolarization ratio (ρ) and coincident measurements of the particulate backscattering ratio (bbp/bp). The black line represents a least-squares exponential fit to the data.

As LiDAR technology becomes increasingly rugged, compact, and inexpensive, the regular deployment of oceanographic LiDAR on a variety of sampling platforms will become an increasingly practical method for characterizing the vertical and horizontal distribution of particles in the ocean. This has the potential to greatly improve our ability to investigate the role of particles in physical and biogeochemical oceanographic processes, especially when sampling constraints limit observations to the surface ocean.

 

Authors:
Brian L. Collister (Old Dominion University)
Richard C. Zimmerman (Old Dominion University)
Charles I. Sukenik (Old Dominion University
Victoria J. Hill (Old Dominion University)
William M. Balch (Bigelow Laboratory for Ocean Sciences)

When marine-terminating glaciers ‘pump’ the ocean

Posted by mmaheigan 
· Wednesday, October 10th, 2018 

How will increasing meltwater from Greenland affect the biogeochemistry of the ocean? Release of meltwater into the ocean has physical and biogeochemical effects on the local water column. With respect to nutrient availability, meltwater supplies the bioessential nutrients iron and silicic acid but is deficient in nitrate and phosphate. However, despite very low meltwater nitrate and phosphate concentrations, pronounced summertime phytoplankton blooms are observed in many, though not all, of Greenland’s large fjord systems. These unusual summertime blooms are associated with meltwater from marine-terminating glaciers. So if the meltwater itself is not supplying nitrate and phosphate that these blooms require, what is the source of the nutrients that support these blooms?

An illustration of how changing the depth of a glacier affects downstream productivity

A recent study published in Nature Communications shows that when meltwater is released below sea level under large marine-terminating glaciers, it rises rapidly towards the surface in buoyant discharge plumes. As these plumes rise, they entrain large quantities of deep, nutrient-rich seawater. This vertical transport, or ‘pumping’, of these nutrients to the surface sustains unusually high summertime productivity in Greenland’s fjords. Conversely, when meltwater is released at the ocean surface, primary production is reduced because the meltwater itself lacks the nitrate and phosphate required to fuel phytoplankton blooms. Consequently, the inland retreat of Greenland’s large marine-terminating glaciers is ultimately bad news for summertime marine phytoplankton communities. As the depth of the marine-terminating glaciers shoals, their associated nutrient ‘pumps’ collapse, which will likely have negative effects on primary production and associated inshore fisheries.

 

Authors:
M.J. Hopwood (GEOMAR)
D. Carroll (Jet Propulsion Laboratory)
T.J. Browning (GEOMAR)
L. Meire (Royal Netherlands Institute for Sea Research and Greenland Climate Research Centre)
J. Mortensen (Greenland Climate Research Centre)
S. Krisch (GEOMAR)
E.P. Achterberg (GEOMAR)

Primary productivity à la mode

Posted by mmaheigan 
· Wednesday, October 10th, 2018 

The presence of large-scale Ekman downwelling is the textbook explanation for low nutrient concentrations, and hence low productivity, in subtropical gyres. However, recent research has suggested that mesoscale eddies oppose and substantially reduce this downwelling, a process known as eddy cancellation (Doddridge et al, 2016). Eddy cancellation represents a substantial alteration to the widely accepted notion of large-scale Ekman downwelling in subtropical gyres, and motivates our study of the processes that determine nutrient concentration within subtropical gyres.

Figure 1: Sensitivity experiments for mode water thickness (hmode) with two values of residual Ekman pumping. a) With no residual Ekman pumping, phosphate concentration responds strongly to mode water thickness. b) When Ekman pumping is strong, phosphate concentration does not depend on mode water thickness. The dashed lines represent transects of climatological phosphate concentration in the euphotic zone of the North Atlantic subtropical gyre (Garcia et al., 2013).

A recent paper published in the Journal of Geophysical Research: Oceans and featured in an MIT News article describes an idealized model for nutrient concentration in subtropical gyres that can account for this reduction in Ekman pumping. The model predicts that surface productivity is sensitive to the thickness of the underlying subtropical mode water layer, provided that the residual Ekman pumping is small (Figure 1). Comparison of this prediction with observations from the Bermuda Atlantic Time series Study (BATS) shows that surface productivity increases as the thickness of the underlying mode water increases (Figure 2), as predicted by the idealized model in the absence of substantial Ekman pumping.

Figure 2: Annually averaged primary productivity and mode water thickness from the BATS dataset. The linear fit between mode water thickness and primary productivity is statistically significant (p ≈ 0.027) and explains 19.5% of the variance in primary productivity.

The observed relationship between productivity and mode water thickness at BATS is consistent with a small residual Ekman pumping, indicating highly effective eddy cancellation in the subtropical North Atlantic. Previous research (Palter et al., 2005) has suggested that as the subtropical mode water layer thickens, it blocks nutrient entrainment from below, resulting in lower productivity in the euphotic zone. However, this study suggests that a thicker subtropical mode water layer actually increases the surface nutrient concentrations by promoting more effective recycling of nutrients within the gyre. With a thicker mode water layer, more of the nutrients in the particulate flux are remineralized before they pass through the thermocline and become isolated from the surface ocean. This means that a thicker mode water layer leads to higher nutrient concentrations and supports primary productivity in subtropical gyres. This represents a fundamental change in our understanding of how nutrients are supplied to the surface waters of subtropical gyres.

Authors:
Edward Doddridge (Department of Earth, Atmospheric and Planetary Sciences, MIT)
David Marshall (Atmospheric, Oceanic & Planetary Physics, University of Oxford)

See the Eos spotlight on this research

Improved method to identify and reduce uncertainties in marine carbon cycle predictions

Posted by mmaheigan 
· Wednesday, September 26th, 2018 

Improved method to identify and reduce uncertainties in marine carbon cycle predictions

How well do contemporary Earth System Models (ESMs) represent the dynamics of the modern day ocean? Often we question the fidelity of biological and chemical processes represented in these ESMs. The fact is representations of biogeochemical processes in models are plagued with some degree of uncertainties; therefore, identifying and reducing such deficiencies could advance ESM development and improve model predictions.

An overview of several models with respect to each of the variables, using absolute (left) and relative (right) scores to determine the degree of uncertainty in relation to referenced datasets.

 

A recent publication in Atmosphere described the ongoing efforts to develop the International Ocean Model Benchmarking (IOMB) package to evaluate ESM skill sets in simulating marine biogeochemical variables and processes. Model performances were scored based on how well they captured the distribution and variability contained in high-quality observational datasets. The authors highlighted systematic model–data benchmarking as a technique to identify ocean model deficiencies, which could provide a pathway to improving representations of sub-grid-scale parameterizations. They have scaled the absolute score from zero to unity, where the red color tends toward zero to quantify weaknesses in the skill set of a particular model in capturing values from the observational datasets. On the other side of the spectrum, the green color signifies considerable temporal and spatial overlap between the predicted and the observational values. The authors also present the standard score to show the relative scores within two standard deviations from the model mean. The benchmarking package was employed in the published study to assess marine biogeochemical process representations, with a focus on surface ocean concentrations and sea–air fluxes of dimethylsulfide (DMS). The production and emission of natural aerosols remain one of the major limitations in estimating global radiative forcing. Appropriate representation of aerosols in the marine boundary layer (MBL) is essential to reduce uncertainty and provide reliable information on offsets to global warming. Results show that model–data biases increased as DMS enters the MBL, with models over-predicting sea surface concentrations in the productive region of the eastern tropical Pacific by almost a factor of two and the sea–air fluxes by a factor of three. The associated uncertainties with oceanic carbon cycle processes may be additive or antagonistic; in any case, a constructive effort to disentangle the subtleties begins with an objective benchmarking effort, which is focused specifically on marine biogeochemical processes. The tool in development will ensure we satisfy some of the Model Intercomparison Project (MIP) benchmarking needs for the sixth phase of Coupled Model Intercomparison Project (CMIP6).

 

Authors:
Oluwaseun Ogunro (ORNL)
Scott Elliott (LANL)
Oliver Wingenter (New Mexico Tech)
Clara Deal (University of Alaska)
Weiwei Fu (UC Irvine)
Nathan Collier (ORNL)
Forrest M. Hoffman (ORNL)

Physics shed new light on microbial filter-feeding

Posted by mmaheigan 
· Wednesday, September 26th, 2018 

Microbial filter-feeders actively filter water for bacteria-sized prey, but hydrodynamic theory predicts that their filtration rate should be one order of magnitude lower than what they realize.   What is missing in our knowledge and modeling of these key components of aquatic food webs?

In a recent study published in PNAS, Nielsen et al. (2017) used a combination of microscopy observations, particle tracking, and analytical and computational fluid dynamics (CFD) to shed light on the physics of microbial filter-feeding. They found that analytical and computational fluid dynamic estimates agree that the observed filtration rate cannot be realized given the known morphology and flagellum kinematics. The estimates consistently fall one order of magnitude short of observed filtration rates. This led the authors to suggest that their study organism, the choanoflagellate Diaphanoeca grandis, has a so-called ‘flagellar vane’, a sheet-like extension of the flagellum seen in some members of the choanoflagellate sister group, the marine sponges. This structure would fundamentally change the physics of the filtration process, and the authors found that both the analytical and the computational estimates match observed filtration rates when such a structure is included.

Left: Choanoflagellate model morphology showing the protoplast (cell) in orange, the filter comprised of microvilli (black), the lorica and chimney (red) and the flagellum with vane (blue). Right: Experimentally observed near-cell flow field vs. flow field modelled using computational fluid dynamics including a flagellar vane. The filter cross-section is here shown in green. The modelled flow field provides a good match with the observed flow field. Without a flagellar vane, the model flow field is at least an order of magnitude weaker. This leads to the suggestion that a flagellar vane is needed to account for the observed flow field and clearance rate.

 

The new insights allow the authors to generalize about the trade-offs involved in microbial filtering, which is important to our understanding of the microbial loop in planktonic food webs. The results are of even wider interest since choanoflagellates are believed to be the evolutionary ancestors of all multicellular animals, many of which include cells that are fundamentally identical to choanoflagellates (e.g., the simple cuboidal epithelium cells of kidneys). Thus, microscale filtering not only happens in every single drop of seawater, it also happens inside most animals.

Learn more here.

Authors:
Lasse Tor Nielsen (National Institute of Aquatic Resources and Centre for Ocean Life, Technical University of Denmark)
Seyed Saeed Asadzadeh (Department of Mechanical Engineering, Technical University of Denmark)
Julia Dölger (Department of Physics and Centre for Ocean Life, Technical University of Denmark)
Jens H. Walther (Department of Mechanical Engineering, Technical University of Denmark, Denmark and Swiss Federal Institute of Technology Zürich, ETH Zentrum)
Thomas Kiørboe (National Institute of Aquatic Resources and Centre for Ocean Life, Technical University of Denmark)
Anders Andersen (Department of Physics and Centre for Ocean Life, Technical University of Denmark)

Shelf-wide pCO2 increase across the South Atlantic Bight

Posted by mmaheigan 
· Thursday, August 2nd, 2018 

Relative to their surface area, coastal regions represent some of the largest carbon fluxes in the global ocean, driven by numerous physical, chemical and biological processes. Coastal systems also experience human impacts that affect carbon cycling, which has large socioeconomic implications. The highly dynamic nature of these systems necessitates observing approaches and numerical methods that can both capture high-frequency variability and delineate long-term trends.

Figure 1: The South Atlantic Bight (SAB) was divided into four sections using isobaths: the coastal zone (0 to 15 m), the inner shelf (15 to 30 m), the middle shelf (30 to 60 m), and the outer shelf (60 m and beyond). The X’s indicate the locations of the Gray’s Reef mooring (southern X) and the Edisto mooring (northern X).

In two recent studies using mooring- and ship-based ocean CO2 system data, authors observed that pCO2 is increasing from the coastal zone to the outer shelf of the South Atlantic Bight at rates greater than the global average oceanic and atmospheric increase (~1.8 µatm y-1). In recent publications in Continental Shelf Research and JGR-Oceans, the authors analyzed pCO2 data from 46 cruises (1991-2016) using a novel linear regression technique to remove the seasonal signal, revealing an increase in pCO2 of 3.0-3.7 µatm y-1 on the outer and inner shelf, respectively. Using a Generalized Additive Mixed Model (GAMM) approach for trend analysis, authors observed that the rates of increase were slightly higher than the deseasonalization technique, yielding pCO2 increases of 3.3 to 4.5 µatm y-1 on the outer and inner shelf, respectively. The reported pCO2 increases result in potential pH decreases of -0.003 to -0.004 units y-1.

Figure 2: The time series of fCO2 in the four regions of the SAB (cruise observations) and from the Gray’s Reef mooring on the inner shelf indicate an increase across the shelf. These data are the observed values, however, the trend lines for each time series are calculated using deseasonalized values using the reference year method.

Analysis of the pCO2 time-series from the Gray’s Reef mooring (using a NOAA Moored Autonomous pCO2 system from July 2006 -July 2015) yielded a rate of increase (3.5 ± 0.9 µatm y-1) that was comparable to the cruise data on the inner shelf (3.7 ± 2.2 and 4.5 ± 0.6 µatm y-1, linear and GAMM methods, respectively). Validation data collected at the mooring suggest that underway data from cruises and the moored data are comparable. Neither thermal processes nor atmospheric dissolution (the primary driver of oceanic acidification) can explain the observed pCO2 increase and concurrent pH decrease across the shelf. Unlike the middle and outer shelves, where an increase in SST could account for up to 1.1 µatm y-1 of the observed pCO2 trend, there is no thermal influence in the coastal zone and inner shelf. While 1.8 µatm y-1 could be attributed to the global average atmospheric increase, the remainder is likely due to transport from coastal marshes and in situ biological processes.  As the authors have shown, the increasing coastal and oceanic trend in pCO2 can lead to a decrease in pH, especially if there is no increase in buffering capacity.  More acidic waters can have a long term affect on coastal ecosystem services and biota.

Also see Eos Editor’s Vox on this research by Peter Brewer https://eos.org/editors-vox/coastal-ocean-warming-adds-to-co2-burden

Authors:

Multidecadal fCO2 Increase Along the United States Southeast Coastal Margin (JGR-Oceans)
Janet J. Reimer (University of Delaware)
Hongjie Wang (Texas A &M University – Corpus Christi)
Rodrigo Vargas (University of Delaware)
Wei-Jun Cai (University of Delaware)

And

Time series pCO2 at a coastal mooring: Internal consistency, seasonal cycles, and interannual variability (Continental Shelf Research)
Janet J. Reimer (University of Delaware)
Wei-Jun Cai (University of Delaware; University of Georgia)
Liang Xue (University of Delaware; First Institute of Oceanography, China)
Rodrigo Vargas (University of Delaware)
Scott Noakes (University of Georgia)
Xinping Hu (Texas A &M University – Corpus Christi)
Sergio R. Signorini (Science Applications International Corporation)
Jeremy T. Mathis (NOAA Arctic Research Program)
Richard A. Feely (NOAA Pacific Marine Environmental Laboratory)
Adrienne J. Sutton (NOAA Pacific Marine Environmental Laboratory; University of Washington)
Christopher Sabine (University of Hawaii Manoa)
Sylvia Musielewicz (NOAA Pacific Marine Environmental Laboratory; University of Washington)
Baoshan Chen (University of Delaware; University of Georgia)
Rik Wanninkhof (NOAA Atlantic Oceanographic and Meteorological Laboratory)

Marine Snowfall at the Equator

Posted by mmaheigan 
· Thursday, July 19th, 2018 

The continual flow of organic particles such as dead organisms and fecal material towards the deep sea is called “marine snow,” and it plays an important role in the ocean carbon cycle and climate-related processes. This snowfall is most intense where high primary production can be observed near the surface. This is the case along the equator in the Pacific and Atlantic Oceans. However, it is not well known how particles are distributed at depth and which processes influence this distribution. A recent study published in Nature Geoscience involved the use of high-resolution particle density data using the Underwater Vision Profiler (UVP) from the equatorial Atlantic and Pacific Oceans down to a depth of 5,000 meters, revealing that several previously accepted ideas on the downward flux of particles into the deep sea should be revisited.

Figure 1. The Underwater Vision Profiler (UVP) during a trial in the Kiel Fjord. The UVP provided crucial data for the new study. Photo: Rainer Kiko, GEOMAR

 

It is typically assumed that the largest particle density can be found close to the surface and that density attenuates continuously with depth. However, high-resolution particle data show that density increases again in the 300-600-meter depth range. The authors attribute this observation to the daily migratory behavior of organisms such as zooplankton that retreat to these depths during the day, contributing to the particle load via defecation and mortality.

Another surprising result is the observation of many small particles below 1,000 meters depth that contribute a large fraction of the bathypelagic particle flux. This observation counters the general assumption, especially in many biogeochemical models, that particle flux at depth comprises fast sinking particles such as fecal pellets. Diminished remineralization rates of small particles or increased disaggregation of larger particles may contribute to the elevated small particle fluxes at this depth.

Figure 2. Zonal current velocity and Particulate Organic Carbon (POC) content across the equatorial Atlantic at 23˚W as observed in November 2012. From left to right: Zonal current velocity, POC content in small particle fraction and POC content in large particle fraction (adapted from Kiko et al. 2017).

 

This study highlights the importance of coupled biological and physical processes in understanding and quantifying the biological carbon pump. Further work on this important topic can now also be submitted to the new Frontiers in Marine Science research topic “Zooplankton and Nekton: Gatekeepers of the Biological Pump” (https://www.frontiersin.org/research-topics/8114/zooplankton-and-nekton-gatekeepers-of-the-biological-pump; Co-editors R. Kiko, M. Iversen, A. Maas, H. Hauss and D. Bianchi). The research topic welcomes a broad range of contributions, from individual-based process studies, to local and global field observations, to modeling approaches to better characterize the role of zooplankton and nekton for the biological pump.

 

Authors:
R. Kiko (GEOMAR)
A. Biastoch (GEOMAR)
P. Brandt (GEOMAR, University of Kiel)
S. Cravatte (LEGOS, University of Toulouse)
H. Hauss (GEOMAR)
R. Hummels (GEOMAR)
I. Kriest (GEOMAR)
F. Marin (LEGOS, University of Toulouse)
A. M. P. McDonnell (University of Alaska Fairbanks)
A. Oschlies (GEOMAR)
M. Picheral (Laboratoire d’Océanographie de Villefranche-sur-Mer, Observatoire Océanologique)
F. U. Schwarzkopf (GEOMAR)
A. M. Thurnherr (Lamont-Doherty Earth Observatory,)
L. Stemmann (Sorbonne Universités, Observatoire Océanologique)

Long-term coastal data sets reveal unifying relationship between oxygen and pH fluctuations

Posted by mmaheigan 
· Thursday, June 7th, 2018 

Coastal habitats are critically important to humans, but without consistent and reliable observations we cannot understand the direction and magnitude of unfolding changes in these habitats. Environmental monitoring is therefore a prescient—yet still undervalued—societal service, and no effort better exemplifies this than the work conducted within the National Estuarine Research Reserve System (NERRS). NERRS is a network of 29 U.S. estuarine sites operated as a partnership between NOAA and the coastal states. NERRS has established a system-wide monitoring program with standardized instrumentation, protocols, and data reporting to guide consistent and comparable data collection across all NERRS sites. This has resulted in high-quality, comparable data on short- to long-term changes in water quality and biological systems to inform effective coastal zone management.

Figure 1: Using dissolved oxygen and salinity, monthly mean pH can be predicted within and across coastal systems due to the unifying metabolic coupling of oxygen and pH.

 

In a recent study published in Estuaries and Coasts, Baumann and Smith (2017) used a subset of this unique data set to analyze short- and long-term variability in pH and dissolved oxygen (DO) at 16 NERRS sites across the U.S. Atlantic, Caribbean, Gulf of Mexico, and Pacific coasts (> 5 million data points). They observed that large, metabolically driven fluctuations of pH and DO are indeed a unifying feature of nearshore habitats. Furthermore, mean pH or mean diel pH fluctuations can be predicted across habitats simply from salinity and oxygen levels/fluctuations (Fig.1). These results provide strong empirical evidence that common metabolic principles drive diel to seasonal pH and DO variations within and across a diversity of estuarine environments. As expected, the study did not yield interannual, monotonic trends in nearshore pH conditions; rather, interannual fluctuations were of similar magnitude to the pH decrease predicted for the average surface ocean over the next three centuries (Fig.2). Correlations of weekly anomalies of pH, oxygen, and temperature yielded strong empirical support for the hypothesis that coastal acidification—in addition to being driven by eutrophication and atmospheric CO2 increases—is exacerbated by warming, likely via increased community respiration.

Figure 2: Interannual variations in temperature, pH, and dissolved oxygen (DO) anomalies in 16 NERRS sites across the US Atlantic, Gulf of Mexico, Caribbean, and Pacific coasts.

Analyses of these long-term data sets have provided important insights on biogeochemical variability and underlying drivers in nearshore environments, highlighting the value and utility of long-term monitoring efforts like NERRS. Sustained, high-quality data sets in these nearshore environments are essential for the study of environmental change and should be prioritized by funding agencies. The observed metabolically driven pH and DO fluctuations suggest that local measures to reduce nutrient pollution can be an effective management tool in support of healthy coastal environments, a boon for both the habitats and humans.

 

Authors:
Hannes Baumann (University of Connecticut)
Erik M. Smith (North Inlet-Winyah Bay National Estuarine Research Reserve, University of South Carolina)

Science Highlight guidelines

Posted by mmaheigan 
· Friday, May 25th, 2018 

Your science highlight should use a narrative style and active voice to engage the reader (no verbatim sentences from your abstract or paper).

Your target audience is a broad scientific readership. You may submit one figure that conveys the key point of the paper, with a succinct caption. The figure (separate high res file) must be modified slightly from its published version to avoid copyright issues.

The text should include the following:

- A catchy title to draw in your reader

- Opening statement highlighting an unknown or a question (1-2 sentences)

- Key results/findings and approaches (with link to article) (3-4 sentences)

- What are the broader implications of this work? Why should federal/state/local gov't, funding agencies, citizens, stakeholders, educators, etc. care?  (1-2 sentences)

- Author name(s) and affiliation(s) - Style: Sam Smyth (University of Carbon)

- Twitter handles of authors and/or labs/institutions

Short backstories are welcome!

We schedule highlights as received and go through one round of editing before publication. Generally it's 2-3 months between sending a highlight and the next open publication date due to current volume. We look forward to receiving your piece! Questions?

Unexpected acidification of deep waters in the Sea of Japan due to global warming

Posted by mmaheigan 
· Tuesday, May 22nd, 2018 

Oceans worldwide are warming up, and thermohaline circulation is expected to slow down. At the same time, ocean acidity is increasing due to the influx of anthropogenic carbon dioxide (CO2) from the atmosphere, a phenomenon called ocean acidification that has primarily been documented in shallow waters. In general, deeper waters contain less anthropogenic CO2, but predicted reductions in ventilation of deep waters may impact deep ocean chemistry, as described in a recent study in Nature Climate Change.

Figure caption: Secular trend of total scale pH at in-situ temperature and pressure at various depths between 1965 and 2015 in the Sea of Japan.

The Sea of Japan is a marginal sea with its own deep- and bottom-water formation that maintains relatively elevated oxygen levels. However, time-series data from 1965-2015 (the longest time-series available) reveal that oxygen concentrations in these deep waters are declining, indicating a reduction in ventilation that increases their residence time. As organic matter decomposition in these waters continues to accumulate more CO2, the pH decreases. As a result, the acidification rate near the bottom of the Sea of Japan is 27% higher than at the surface. As a miniature ocean with its own deep- and bottom-water formation, the Sea of Japan provides insight into how future warming might alter deep-ocean ventilation and chemistry.

 

Authors:
Chen-Tung Arthur Chen (National SunYat-sen University, Taiwan and Second Institute of Oceanography, China)
Hon-Kit Lui (National SunYat-sen University and Taiwan Research Institute)
Chia-Han Hsieh (National SunYat-sen University, Taiwan)
Tetsuo Yanagi (International Environmental Management of Enclosed Coastal Seas Center, Japan)
Naohiro Kosugi (Japan Meterological Agency)
Masao Ishii (Japan Meterological Agency)
Gwo-Ching Gong (National Taiwan Ocean University)

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