Archive for time-series – Page 2

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)

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)

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)

Lasers shed light on giant larvacean filtration impact on the ocean’s biological pump

Posted by mmaheigan 
· Thursday, January 4th, 2018 

To accurately assess the impacts of climate change, we need to understand how atmospheric carbon is transported from surface waters to the deep sea. Grazers and filter feeders drive the ocean’s biological pump as they remove and sequester carbon at various rates. This pump extends down into the midwater realm, the largest habitat on earth. Giant larvaceans are fascinating and enigmatic occupants of the upper 400 m of the water column, where they build complex filtering structures out of mucus that can reach diameters greater than 1 m in longest dimension (Figure 1A). Because of the fragility of these structures, direct measurements of filtration rates require us to study them in situ. We developed DeepPIV, an ROV-deployable instrument (Figure 1B) to directly measure fluid motion and filtration rates in situ (Figure 1C).

Figure 1. (A) Traditional view of a giant larvacean illuminated by white ROV lights. (B) DeepPIV instrument is seen attached to Monterey Bay Aquarium Research Institute’s (MBARI) MiniROV. (C) DeepPIV-illuminated interior view of a giant larvacean house, where particle motion in ambient seawater serves as a proxy for fluid motion. White arrows in (A) and (C) indicate larvacean head/trunk; white arrow in (B) indicates DeepPIV.

The filtration rates we measured for giant larvaceans are far greater than for any other zooplankton filter feeder. When combined with abundance data from a 22-year time series, the grazing impact of giant larvaceans indicates that within 13 days, they can filter the total volume of water within their habitable depth range (~100-300 m; based on maximum abundance and measured filtration rates). Our results reveal that the contribution of giant larvaceans to vertical carbon flux is much greater than previously thought. Small larvaceans, which are present in the water column in even larger quantities than giant larvaceans, may also have a measurable impact on carbon fluxes. New technologies such as DeepPIV are yielding more quantitative observations of midwater filter feeders, which is improving our understanding of the roles that deep-water biota play in the long-term removal of carbon from the atmosphere.

Read the full journal article: http://advances.sciencemag.org/content/3/5/e1602374.full

Authors: (All at MBARI)
Kakani Katija
Rob E. Sherlock
Alana D. Sherman
Bruce H. Robison

Subtropical gyre productivity sustained by lateral nutrient transport

Posted by Katherine Joyce 
· Saturday, November 5th, 2016 

Vertical processes are thought to dominate nutrient resupply across the ocean, however estimated vertical fluxes are insufficient to sustain observed net productivity in the thermally stratified subtropical gyres. A recent study by Letscher et al. (2016) published in Nature Geoscience used a global biogeochemical ocean model to quantify the importance of lateral transport and biological uptake of inorganic and organic forms of nitrogen and phosphorus to the euphotic zone over the low-latitude ocean. Lateral nutrient transport is a major contributor to subtropical nutrient budgets, supplying a third of the nitrogen and up to two-thirds of the phosphorus needed to sustain gyre productivity. Half of the annual lateral nutrient flux occurs during the stratified summer and fall months, helping to explain seasonal patterns of net community production at the time-series sites near Bermuda and Hawaii. Figure from Letscher et al. (2016).

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