Jessica N. Cross

Coupling primary production and terrestrial runoff to ocean acidification and carbonate mineral suppression in the eastern Bering Sea

Water column pH and carbonate mineral saturation states were calculated from dissolved inorganic carbon (DIC) and total alkalinity data collected over the eastern Bering Sea shelf in the spring and summer of 2008. The saturation states (?) of the two most important carbonate minerals, calcite (?calcite) and aragonite (?aragonite) were strongly coupled to terrestrial runoff from the Yukon and Kuskokwim rivers, primary production in the surface waters, and remineralization of organic matter at depth over the shelf. In spring, before ice melt occurred, pH over the shelf was largely confined to a range of 7.9–8.1 and ?calcite and ?aragonite ranged from 1.5 to 3.0 and 0.8 to 2.0, respectively. At the stations closest to river outflows, aragonite was undersaturated in the water column from the surface to the bottom. During the summer sea ice retreat, high rates of primary production consumed DIC in the mixed layer, which increased pH and ?calcite and ?aragonite. However, ?calcite and ?aragonite decreased by ?0.3 in the bottom waters over the middle and outer shelf. Over the northern shelf, where export production is highest, ?aragonite decreased by ?0.35 and became highly undersaturated. The observed suppression and undersaturation of ?calcite and ?aragonite in the eastern Bering Sea are correlated with anthropogenic carbon dioxide uptake into the ocean and will likely be exacerbated under business-as-usual emission scenarios. Therefore, ocean acidification could threaten some benthic and pelagic calcifying organisms across the Bering Sea shelf in the coming decades.

The role of ocean acidification in systemic carbonate mineral suppression in the Bering Sea

Ocean acidification driven by absorption of anthropogenic carbon dioxide (CO2) from the atmosphere is now recognized as a systemic, global process that could threaten diverse marine ecosystems and a number of commercially important species. The change in calcium carbonate (CaCO3) mineral saturation states (?) brought on by the reduction of seawater pH is most pronounced in high latitude regions where unique biogeochemical processes create an environment more susceptible to the suppression of ? values for aragonite and calcite, which are critical to shell building organisms. New observations from the eastern Bering Sea shelf show that remineralization of organic matter exported from surface waters rapidly increases bottom water CO2 concentrations over the shelf in summer and fall, suppressing ? values. The removal of CO2 from surface waters by high rates of phytoplankton primary production increases ? values between spring and summer, but these increases are partly counteracted by mixing with sea ice melt water and terrestrial river runoff that have low ? values. While these environmental processes play an important role in creating seasonally low saturation states, ocean uptake of anthropogenic CO2 has shifted ? values for aragonite to below the saturation horizon in broad regions across the shelf for at least several months each year. Furthermore, we also report that calcite became undersaturated in September of 2009 in the bottom waters over the shelf. The reduction in CaCO3 mineral saturation states could have profound implications for several keystone calcifying species in the Bering Sea, particularly the commercially important crab fisheries.

Sea‐air CO2 exchange in the western Arctic coastal ocean

The biogeochemical seascape of the western Arctic coastal ocean is in rapid transition. Changes in sea ice cover will be accompanied by alterations in sea-air carbon dioxide (CO2) exchange, of which the latter has been difficult to constrain owing to sparse temporal and spatial data sets. Previous assessments of sea-air CO2 flux have targeted specific subregional areas of the western Arctic coastal ocean. Here a holistic approach is taken to determine the net sea-air CO2 flux over this broad region. We compiled and analyzed an extensive data set of nearly 600,000 surface seawater CO2 partial pressure (pCO2) measurements spanning 2003 through 2014. Using space-time colocated, reconstructed atmospheric pCO2 values coupled with the seawater pCO2 data set, monthly climatologies of sea-air pCO2 differences (ΔpCO2) were created on a 0.2° latitude × 0.5° longitude grid. Sea-air CO2 fluxes were computed using the ΔpCO2 grid and gas transfer rates calculated from climatology of wind speed second moments. Fluxes were calculated with and without the presence of sea ice, treating sea ice as an imperfect barrier to gas exchange. This allowed for carbon uptake by the western Arctic coastal ocean to be assessed under existing and reduced sea ice cover conditions, in which carbon uptake increased 30% over the current 10.9 ± 5.7 Tg C (1 Tg = 1012 g) yr−1 of sea ice-adjusted exchange in the region. This assessment extends beyond previous subregional estimates in the region in an all-inclusive manner and points to key unresolved aspects that must be targeted by future research.

Carbon Biogeochemistry of the Western Arctic: Primary Production, Carbon Export and the Controls on Ocean Acidification

The Arctic Ocean is an important sink for atmospheric carbon dioxide (CO2) with a recent estimate suggesting that the region accounts for as much as 15 % of the global uptake of CO2. The western Arctic Ocean, in particular is a strong ocean sink for CO2, especially in the Chukchi Sea during the open water season when rates of primary production can reach as high as 150 g C m−2. The Arctic marine carbon cycle, the exchange of CO2 between the ocean and atmosphere, and the fate of carbon fixed by marine phytoplankton appear particularly sensitive to environmental changes, including sea ice loss, warming temperatures, changes in the timing and location of primary production, changes in ocean circulation and freshwater inputs, and even the impacts of ocean acidification. In the near term, further sea ice loss and other environmental changes are expected to cause a limited net increase in primary production in Arctic surface waters. However, recent studies suggest that these enhanced rates of primary production could be short lived or not occur at all, as warming surface waters and increases in freshwater runoff and sea ice melt enhance stratification and limit mixing of nutrient-rich waters into the euphotic zone. Here, we provide a review of the current state of knowledge that exists about the rates of primary production in the western Arctic as well as the fate of organic carbon fixed by primary produces and role that these processes play in ocean acidification in the region.

Annual sea‐air CO2 fluxes in the Bering Sea: Insights from new autumn and winter observations of a seasonally ice‐covered continental shelf

High-resolution data collected from several programs have greatly increased the spatiotemporal resolution of pCO2(sw) data in the Bering Sea, and provided the first autumn and winter observations. Using data from 2008 to 2012, monthly climatologies of sea-air CO2 fluxes for the Bering Sea shelf area from April to December were calculated, and contributions of physical and biological processes to observed monthly sea-air pCO2 gradients (?pCO2) were investigated. Net efflux of CO2 was observed during November, December, and April, despite the impact of sea surface cooling on ?pCO2. Although the Bering Sea was believed to be a moderate to strong atmospheric CO2 sink, we found that autumn and winter CO2 effluxes balanced 65% of spring and summer CO2 uptake. Ice cover reduced sea-air CO2 fluxes in December, April, and May. Our estimate for ice-cover corrected fluxes suggests the mechanical inhibition of CO2 flux by sea-ice cover has only a small impact on the annual scale (<2%). An important data gap still exists for January to March, the period of peak ice cover and the highest expected retardation of the fluxes. By interpolating between December and April using assumptions of the described autumn and winter conditions, we estimate the Bering Sea shelf area is an annual CO2 sink of ?6.8 Tg C yr?1. With changing climate, we expect warming sea surface temperatures, reduced ice cover, and greater wind speeds with enhanced gas exchange to decrease the size of this CO2 sink by augmenting conditions favorable for greater wintertime outgassing.

Innovative technology development for Arctic Exploration

The US Arctic and sub-Arctic regions are rapidly changing, creating potentially large impacts to marine ecosystems and ecosystem services. However, much of the current observing technology is ill suited to fully quantify these dynamic changes. The harsh, remote environment, expansive area, and extremely fine scale features present clear barriers to the efficient collection of effective environmental intelligence. In order to meet these challenges, NOAAs Pacific Marine Environmental Laboratory, with support from Ocean and Atmospheric Research Division, has created the Innovative Technology for Arctic Exploration (ITAE) program to facilitate the development of new autonomous platforms and high-resolution sensing technologies that may be able to address this critical gap in mission capabilities. During the programs primary field testing year, ITAE successfully completed two large-scale research missions in the Bering and Chukchi Seas involving multiple new Arctic-capable platforms, including the Saildrone unmanned autonomous surface vehicle (Saildrone, Inc.), the Profiling Crawler (PRAWLER; NOAA-PMEL), a moored instrument drastically improving vertical resolution of data collection; and the Expendable Ice Tracking (EXIT) Floats, which allow for under-ice data collection (NOAA-PMEL). Through these platforms, ITAE also tested a variety of novel sensing technologies, such as the recently developed microfluidic nitrate sensor, the Lab-on-a-Chip (National Oceanography Centre, University of Southampton). Together, these developments helped to assess important and previously inaccessible aspects of the sea ice melt season. However, important technical challenges remain, including autonomous ecosystem assessment tools that could effectively monitor and aid management of the regions multi-billion dollar annual commercial and subsistence fishing industries.

Role of Technology in Ocean Acidification: Monitoring, Water-Quality Impairments, CO 2 Mitigation, and Machine Learning

Ocean acidification (OA), or the reduction in the pH of the ocean, is driven by increasing carbon dioxide concentration in the atmosphere and local pollution. There is already evidence of the detrimental impact of OA on marine organisms. As further increases in atmospheric CO 2 and changes in water quality are expected, it is crucial to develop and implement advanced technologies that enable better monitoring, allow for understanding of adaptation potential of the organisms, and facilitate the use of mitigation strategies toward predicted environmental changes. Collaboration of marine and computer scientists, engineers, and citizens is needed to develop innovative sustainable technologies to mitigate and reduce future increase of CO 2 .

NOAA’s Alaska Ocean Acidification Research Plan for FY18-FY20.

Dissolution of anthropogenic CO2 has reduced global mean surface water 0.1 pH units below preindustrial levels, a change of about 26% (Caldeira and Wickett 2003, Orr et al. 2005). In addition, deep oceanic waters are depleted in carbonate due to respiration resulting in a saturation depth below which calcium carbonate dissolves. Thus, decreased carbonate ion concentration hinders the formation of shells and support structures by some calcifying organisms (Caldeira and Wickett 2003, Feely et al. 2004, Orr et al. 2005). Crustaceans are calcifying organisms that are critical to marine food webs and support important commercial fisheries. In the North Pacific Ocean, where the saturation depth is relatively shallow due to the cold temperature and age of advected deep water masses, Golden king crab (Lithodes aequispinus), snow crab (Chionoecetes opilio), Tanner crab (Chionoecetes bairdi), and red king crab (Paralithodes camtschaticus) are ecologically and economically important crustaceans. The influence of lower pH and decreased carbonate ion concentration in seawater on the condition, survival, and shell calcium carbonate content of snow crabs in Alaska are unknown. Acidified waters can have a significant effect on the development (Findlay et al. 2009, Parker et al. 2009), development time (Findlay et al. 2009), viability (Kurihara et al. 2004a), and even behavior (Ellis et al. 2009) of the embryos of marine invertebrates (though see Arnold et al. 2009). Further, acidified waters can reduce fertilization success (Parker et al. 2009), the hatching success of embryos (Kurihara et al. 2004a), and the fecundity of females (Kurihara et al. 2004b). We propose to conduct experimental research on golden king crab juveniles, which are currently available from previous experimental treatments on embryological development and larval survival. Next we propose to initiate studies on snow crab. Snow crab culturing is more difficult than the other species, however, the important role of snow crab ecologically and economically to Alaska coastal communities necessitates that we test the effects of OA on this species. Snow crab adults (ovigerous females) will be included in experiments in the summer of 2014 so that embryological studies can be conducted in FY15. Further, snow crab will be treated similarly to its congener, Tanner crab, so that direct comparisons can be made to the physiological response of