Lisa L. Robbins

Baseline Monitoring of the Western Arctic Ocean Estimates 20% of Canadian Basin Surface Waters Are Undersaturated with Respect to Aragonite

Marine surface waters are being acidified due to uptake of anthropogenic carbon dioxide, resulting in surface ocean areas of undersaturation with respect to carbonate minerals, including aragonite. In the Arctic Ocean, acidification is expected to occur at an accelerated rate with respect to the global oceans, but a paucity of baseline data has limited our understanding of the extent of Arctic undersaturation and of regional variations in rates and causes. The lack of data has also hindered refinement of models aimed at projecting future trends of ocean acidification. Here, based on more than 34,000 data records collected in 2010 and 2011, we establish a baseline of inorganic carbon data (pH, total alkalinity, dissolved inorganic carbon, partial pressure of carbon dioxide, and aragonite saturation index) for the western Arctic Ocean. This data set documents aragonite undersaturation in ∼20% of the surface waters of the combined Canada and Makarov basins, an area characterized by recent acceleration of sea ice loss. Conservative tracer studies using stable oxygen isotopic data from 307 sites show that while the entire surface of this area receives abundant freshwater from meteoric sources, freshwater from sea ice melt is most closely linked to the areas of carbonate mineral undersaturation. These data link the Arctic Ocean’s largest area of aragonite undersaturation to sea ice melt and atmospheric CO2 absorption in areas of low buffering capacity. Some relatively supersaturated areas can be linked to localized biological activity. Collectively, these observations can be used to project trends of ocean acidification in higher latitude marine surface waters where inorganic carbon chemistry is largely influenced by sea ice meltwater.

Variability of the carbonate chemistry in a shallow, seagrass-dominated ecosystem: implications for ocean acidification experiments

Open ocean observations have shown that increasing levels of anthropogenically derived atmospheric CO2 are causing acidification of the world’s oceans. Yet little is known about coastal acidification and studies are just beginning to characterise the carbonate chemistry of shallow, nearshore zones where many ecologically and economically important organisms occur. We characterised the carbonate chemistry of seawater within an area dominated by seagrass beds (Saint Joseph Bay, Florida) to determine the extent of variation in pH and pCO2 over monthly and daily timescales. Distinct diel and seasonal fluctuations were observed at daily and monthly timescales respectively, indicating the influence of photosynthetic and respiratory processes on the local carbonate chemistry. Over the course of a year, the range in monthly values of pH (7.36–8.28), aragonite saturation state (0.65–5.63), and calculated pCO2 (195–2537μatm) were significant. When sampled on a daily basis the range in pH (7.70–8.06), aragonite saturation state (1.86–3.85), and calculated pCO2 (379–1019μatm) also exhibited significant range and indicated variation between timescales. The results of this study have significant implications for the design of ocean acidification experiments where nearshore species are utilised and indicate that coastal species are experiencing far greater fluctuations in carbonate chemistry than previously thought.

Sources, Distributions, and Dynamics of Dissolved Organic Matter in the Canada and Makarov Basins

A comprehensive survey of dissolved organic carbon (DOC) and chromophoric dissolved organic matter (CDOM) was conducted in the Canada and Makarov Basins and adjacent seas during 2010-2012 to investigate the dynamics of dissolved organic matter (DOM) in the Arctic Ocean. Sources and distributions of DOM in polar surface waters were very heterogeneous and closely linked to hydrological conditions. Canada Basin surface waters had relatively low DOC concentrations (69±6 µmol L-1), CDOM absorption (a325: 0.32±0.07 m-1) and CDOM-derived lignin phenols (3±0.4 nmol L-1) and high spectral slope values (S275-295: 31.7±2.3 µm-1), indicating minor terrigenous inputs and evidence of photochemical alteration in the Beaufort Gyre. By contrast, surface waters of the Makarov Basin had elevated DOC (108±9 µmol L-1) and lignin phenol concentrations (15±3 nmol L-1), high a325 values (1.36±0.18 m-1) and low S275-295 values (22.8±0.8 µm-1), indicating pronounced Siberian river inputs associated with the Transpolar Drift and minor photochemical alteration. Observations near the Mendeleev Plain suggested limited interactions of the Transpolar Drift with Canada Basin waters, a scenario favoring export of Arctic DOM to the North Atlantic. The influence of sea-ice melt on DOM was region-dependent, resulting in an increase (Beaufort Sea), a decrease (Bering-Chukchi Seas), and negligible change (deep basins) in surface DOC concentrations and a325 values. Halocline structures differed between basins, and the Canada Basin upper halocline and Makarov Basin halocline were comparable in their average DOC (65-70 µmol L-1) and lignin phenol concentrations (3-4 nmol L-1) and S275-295 values (22.9-23.7 µm-1). Deep-water DOC concentrations decreased by 6-8 µmol L-1 with increasing depth, water mass age, nutrient concentrations, and apparent oxygen utilization. Maximal estimates of DOC degradation rates (0.036-0.039 µmol L-1 yr-1) in the deep Arctic were lower than those in other ocean basins, possibly due to low water temperatures. DOC concentrations in bottom waters (>2500 m; 46±2 µmol L-1) of the Canada and Makarov Basins were slightly lower than those reported for deep waters of the Eurasian Basin and Nordic Seas. Elevated a325 values (by 10-20%) were observed near the seafloor, indicating biological activity in Arctic basin sediments.

Interpreting the role of pH on stable isotopes in large benthic foraminifera

&NA; Large benthic foraminifera (LBF) are prolific producers of calcium carbonate sediments in shallow, tropical environments that are being influenced by ocean acidification (OA). Two LBF species, Amphistegina gibbosa (Order Rotaliida) with low‐Mg calcite tests and Archaias angulatus (Order Miliolida) with high‐Mg calcite tests, were studied to assess the effects of pH 7.6 on oxygen and carbon isotopic fractionation between test calcite and ambient seawater. The &dgr;18O and &dgr;13C values of terminal chambers and of whole adult tests of both species after 6 weeks were not significantly different between pH treatments of 8.0 and 7.6. However, tests of juveniles produced during the 6‐week treatments showed significant differences between &dgr;18O and &dgr;13C values from control (pH 8.0) when compared with the treatment (pH 7.6) for both species. Although each individuals growth was photographed and measured, difficulty in distinguishing and manually extracting newly precipitated calcite from adult specimens likely confounded any differences in isotopic signals. However, juvenile specimens that resulted from asexual reproduction that occurred during the experiments did not contain old carbonate that could confound the new isotopic signals. These data reveal a potential bias in the design of OA experiments if only adults are used to investigate changes in test chemistries. Furthermore, the results reaffirm that different calcification mechanisms in these two foraminiferal orders control the fractionation of stable isotopes in the tests and will reflect decreasing pH in seawater somewhat differently.

Viral Lysis of Photosynthesizing Microbes As a Mechanism for Calcium Carbonate Nucleation in Seawater

Removal of carbon through the precipitation and burial of calcium carbonate in marine sediments constitutes over 70% of the total carbon on Earth and is partitioned between coastal and pelagic zones. The precipitation of authigenic calcium carbonate in seawater, however, has been hotly debated because despite being in a supersaturated state, there is an absence of persistent precipitation. One of the explanations for this paradox is the geochemical conditions in seawater cannot overcome the activation energy barrier for the first step in any precipitation reaction; nucleation. Here we show that virally induced rupturing of photosynthetic cyanobacterial cells releases cytoplasmic-associated bicarbonate at concentrations ~23-fold greater than in the surrounding seawater, thereby shifting the carbonate chemistry toward the homogenous nucleation of one or more of the calcium carbonate polymorphs. Using geochemical reaction energetics, we show the saturation states (Ω) in typical seawater for calcite (Ω = 4.3), aragonite (Ω = 3.1), and vaterite (Ω = 1.2) are significantly elevated following the release and diffusion of the cytoplasmic bicarbonate (Ωcalcite = 95.7; Ωaragonite = 68.5; Ωvaterite = 25.9). These increases in Ω significantly reduce the activation energy for nuclei formation thresholds for all three polymorphs, but only vaterite nucleation is energetically favored. In the post-lysis seawater, vaterites nuclei formation activation energy is significantly reduced from 1.85 × 10−17 J to 3.85 × 10−20 J, which increases the nuclei formation rate from highly improbable (<<1.0 nuclei cm−3 s−1) to instantaneous (8.60 × 1025 nuclei cm−3 s−1). The proposed model for homogenous nucleation of calcium carbonate in seawater describes a mechanism through which the initial step in the production of carbonate sediments may proceed. It also presents an additional role of photosynthesizing microbes and their viruses in marine carbon cycles and reveals these microorganisms are a collective repository for concentrated and reactive dissolved inorganic carbon (DIC) that is currently not accounted for in global carbon budgets and carbonate sediment diagenesis models.

Whiting events in SW Florida coastal waters: a case study using MODIS medium-resolution data

Whitings, floating patches of calcium carbonate mud, have been found in both shallow carbonate banks and freshwater environments around the world. Although these events have been studied for many decades, much of their characteristics remain unknown. Recent sightings of whitings near Ten Thousand Islands, Florida suggest a phenomenon that has not previously been documented in this area. Using medium-resolution (250-m) data collected by the Moderate Resolution Imaging Spectroradiometer (MODIS) from December 2010 to November 2013, we documented whiting events and their spatial and temporal patterns in this region. Classification rules were first established, and then applied to all 474 cloud-free and sun glint-free MODIS images. Whiting occurrences were found between 25°46′N and 25°20′N and less than 40 km from the southwest Florida coastline. Over the 3-year period, whiting occurrence peaked in spring and autumn and reached a minimum during the winter and summer months. Further field and laboratory research are needed to explain driving force(s) behind these events.

Acidification and Increasing CO 2 Flux Associated with Five, Springs Coast, Florida Springs (1991-2014)

Scientists from the South West Florida Management District (SWFWMD) acquired and analyzed over 20 years of seasonally-sampled hydrochemical data from five first-order-magnitude (springs that discharge 2.83 m3 s-1 or more) coastal springs located in west-central Florida. These data were subsequently obtained by the U.S. Geological Survey (USGS) for further analyses and interpretation. The spring study sites (Chassahowitzka, Homosassa, Kings Bay, Rainbow, and Weeki Wachee), which are fed by the Floridan Aquifer system and discharge into the Gulf of Mexico were investigated to identify temporal and spatial trends of pH, alkalinity, partial pressure of carbon dioxide (pCO2) and CO2 flux.

Processes of multibathyal aragonite undersaturation in the Arctic Ocean

During three years of study (2010-2012), the western Arctic Ocean was found to have unique aragonite saturation profiles with up to three distinct aragonite undersaturation zones. This complexity is produced as inflow of Atlantic- and Pacific-derived water masses mix with Arctic-derived waters, which are further modified by physiochemical and biological processes. The shallowest aragonite undersaturation zone, from the surface to ∼ 30 m depth is characterized by relatively low alkalinity and other dissolved ions. Besides local influence of biological processes on aragonite undersaturation of shallow coastal waters, the nature of this zone is consistent with dilution by sea-ice melt and invasion of anthropogenic CO2 from the atmosphere. A second undersaturated zone at ∼ 90-220 m depth (salinity ∼31.8–35.4) occurs within the Arctic Halocline and is characterized by elevated pCO2 and nutrients. The nature of this horizon is consistent with remineralization of organic matter on shallow continental shelves bordering the Canada Basin and the input of the nutrients and CO2 entrained by currents from the Pacific Inlet. Finally, the deepest aragonite undersaturation zone is at greater than 2000 m depth and is controlled by similar processes as deep aragonite saturation horizons in the Atlantic and Pacific Oceans. The comparatively shallow depth of this deepest aragonite saturation horizon in the Arctic is maintained by relatively low temperatures, and stable chemical composition. Understanding the mechanisms controlling the distribution of these aragonite undersaturation zones, and the timescales over which they operate will be crucial to refine predictive models. This article is protected by copyright. All rights reserved.

Response of Florida shelf ecosystems to climate change; from macro to micro scales

U.S. Geological Survey (USGS) research in St. Petersburg, Fla., is focusing attention on marine environments of the Florida shelf at three levels, from regional to estuarine to the individual organism. The USGS is partnering on this project with the Florida Department of Agriculture and Consumer Services (DACS), National Oceanic and Atmospheric Administration (NOAA), and the University of South Florida (USF) in marine studies. The specific goals of these combined efforts are an improved understanding of the effects of ocean acidification on regional carbonate processes, changes in individual estuaries, and organism-level response (fig. 1). This understanding will assist in developing appropriate Federal, State, and local management responses to climate change in coastal areas.

Mapping and vessel-based capabilities

Printed on recycled paper Research Vessel G.K. Gilbert—This 1993 research vessel is a 50-foot, semi-V-hulled Munson Hammerhead with a shallow, 2.5-foot draft. The vessel can operate at 30 knots with three 425-horsepower turbodiesels powering three quiet Hamilton Jets. With all exhaust outlets above the waterline, the vessel is relatively quiet, with an excellent acoustic signal-to-noise ratio to optimize survey data quality. The jet propulsion also eliminates propeller entanglement with sensor cables and improves shallow water access without damage to the boat. Fully-equipped, the R/V Gilbert can simultaneously run sidescan sonar imaging, swath bathymetry, high-resolution bathymetry, and three levels of seismic profiles, while maintaining coring and dive platform capabilities. Houseboats—Two USGS houseboats serve as home base for biological monitoring and extended site-specific data collection. The houseboat, R/V Marjorie Douglas, is a 50-foot aluminum custom-built Clark Boat with 22-inch draft, 200-gallon freshwater carrying capacity, and a 10-day field range. The Marjorie Douglas has a wet-lab and can house a 4-person crew. Houseboats provide basic living facilities, onsite laboratories, 24-hour data collection, and eliminate travel time during extended field sessions. R/V Catboat—This 1999 research vessel is a 26-foot fiberglass Glacier Bay Coastal Runner with Twin Yamaha 115-horsepower engines and a cruising speed of 25 knots. It is used to perform shallow water and nearshore bathymetric surveys, sidescan sonar seafloor imaging, and swath bathymetry surveys. The vessel can cruise at 40 knots fully loaded, enabling daily surveys in large estuaries, lakes, bays, or rivers, and nearshore ocean environments that require long transits. Scientists and engineers from USGS FISC in St. Petersburg prepare a sediment core barrel onboard the R/V Gilbert.