Large Contribution of Pteropods to Shallow CaCO3 Export

The literature on the relative contributions of pelagic calcifying taxa to the global ocean export of CaCO3 is divided. Studies based on deep sediment trap data tend to argue that either foraminifers or coccolithophores, both calcite producers, dominate export. However, the compilations of biomass observations for pteropods, coccolithophores, and foraminifers instead show that pteropods dominate the global ocean calcifier biomass and therefore likely also carbonate export. Here we present a new global ocean biogeochemical model that explicitly represents these three groups of pelagic calcifiers. We synthesize databases of the physiology of the three groups to parameterize the model and then tune the unconstrained parameters to reproduce the observations of calcifier biomass and CaCO3 export. The model can reproduce both these observational databases; however, substantial dissolution of aragonite above the aragonite saturation horizon is required to do so. We estimate a contribution of pteropods to shallow (100 m) export of CaCO3 of at least 33% and to pelagic calcification of up to 89%. The high production‐high dissolution configuration that shows closest agreement with all the observations has a CaCO3 production of 4.7 Pg C/year but CaCO3 export at 100 m of only 0.6 Pg C/year

Salish Sea model: ocean acidification module and the response to regional anthropogenic nutrient sources

Several monitoring programs indicate the presence of lower pH and related changes in carbonate system variables in the Salish Sea. This project expands the existing Salish Sea Model to evaluate carbonate system variables. This project quantifies the influences of regional nutrient sources on acidification. The model accounts for Pacific Ocean upwelled water, regional human nutrient contributions, and air emissions around the Salish Sea. This effort also identifies geographical areas and seasons experiencing greater influence from regional sources of nutrients to Salish Sea waters. Results from this effort indicate that increased dissolved inorganic nitrogen, phytoplankton biomass, and non-algal organic carbon caused by regional anthropogenic nutrient sources can constitute significant contributors to acidification in the Salish Sea

Carbonate chemistry covariation with temperature and oxygen in the Salish Sea and California Current Ecosystems: implications for the design of ocean acidification experiments

A central goal of ocean acidification (OA) research is to understand the ecological consequences that future changes in ocean chemistry will have on marine ecosystems. To address this uncertainty researchers rely heavily on manipulative experiments where biological responses are evaluated across different pCO2 treatments. In coastal systems, however, contemporary carbonate chemistry variability remains only partially characterized and patterns of covariation with other biologically important variables such as temperature and oxygen are rarely evaluated or incorporated into experimental design. Here, we compiled a large carbonate chemistry data set that consists of measurements from multiple moorings and ship-based sampling campaigns from the Salish Sea and larger California Current Ecosystem (CCE). We evaluated patterns of pCO2 variability and highlight important covariation between pCO2, temperature, and oxygen. We subsequently compared environmental pCO2-temperature measurements with conditions maintained in OA experiments that used organisms from the Salish Sea and CCE. By drawing such comparisons, researchers can gain insight into the ecological relevancy of previously published OA experimental designs, but also identify species or life history stages that may already be influenced by contemporary carbonate chemistry conditions. We illustrate the implications that covariation among environmental variables can have for the interpretation of OA experimental results and suggest an approach for developing experimental designs with pCO2 levels that better reflect OA hypotheses while simultaneously recognizing natural covariation with other biologically relevant variables

Vulnerability of Southern ocean pteropods to anthropogenic ocean acidification

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Shell Dissolution of the Pteropod L. helicina in the Puget Sound

The changes in carbonate chemistry driven by ocean acidification (OA) are already evident in the Salish Sea. One consequence of this is the decrease in the carbonate ion concentration. Marine calcifiers use aragonite to build their calcium carbonate shells. Along the West Coast of the U.S., this decrease has been shown to enhance the shell dissolution of pteropods, pelagic gastropods with thin fragile aragonite shells, making them particularly vulnerable to OA. However, very little is known about the state of pteropods in the Puget Sound. This study aims to investigate the state of pteropods based on shell dissolution using scanning electron microscope imaging. The aim of this research is to use pteropods as bioindicators of OA, linking the low aragonite waters of the Puget Sound to observed shell dissolution. Pteropods with severe dissolution have been found in chronically undersaturated locations such as Hood Canal, and are widespread throughout the Puget Sound at the end of the upwelling season in the fall and early winter

Determination of the Anthropogenic Carbon Signal in the Coastal Upwelling Region Along the Washington-Oregon-California Continental Margin

The continental shelf region off the Washington-Oregon-California coast is seasonally exposed to water with a low aragonite saturation state by coastal upwelling of CO2-rich waters. To date, the spatial and temporal distribution of anthropogenic CO2 (Canthro) contribution to the CO2-rich waters is largely unknown. Here we use an adaptation of the linear regression approach described in Feely et al (2008) along with the GO-SHIP Repeat Hydrography data sets from the northeast Pacific to establish an annually updated relationship between Canthro and potential density. This relationship was then used with the NOAA Ocean Acidification Program west coast cruise data sets from 2007, 2011, 2012 and 2013 to determine the spatial variations of Canthro in the upwelled water. Our results show large spatial differences in Canthro in surface waters along the coast with the lowest surface values (40-45 µmol kg-1) in strong upwelling regions of off northern California and southern Oregon and higher values (50-70 µmol kg-1) to the north and south. Canthro contributes an average of about 70% of the increased amount of dissolved inorganic carbon in the upwelled waters at the surface. In contrast, at 50 m the Canthro contribution is approximately 31% and at 100 m it averages about 16%. The remaining contributions are primarily due to respiration processes in the water that was upwelled and transported to coastal regions or underwent respiration processes that occurred locally during the course of the upwelling season. The uptake of Canthro has caused the aragonite saturation horizon to shoal by approximately 30-50 m since preindustrial period so that the undersaturated waters are well within the regions that affect the biological communities on the continental shelf

Pteropod shell dissolution as an indicator for ocean acidification monitoring in the Salish Sea

Pteropods are pelagic marine zooplankton with seasonally high abundances in the Salish Sea, representing an important prey item for variety of economically, ecologically, and culturally important fish species. The thin aragonitic shells of pteropods begin to dissolve when exposed to corrosive undersaturated waters, making them extremely sensitive to ocean acidification conditions. Recently developed methods and interdisciplinary approaches have made it possible to quantify pteropod responses in the natural environment. Because pteropod shell dissolution is both rapid and specific with respect to ocean acidification conditions, measurement of shell dissolution provides a sensitive early warning signal and robust indicator for ocean acidification. We have developed an easy-to-use, cost-effective and rapid technique offering great potential for ocean acidification monitoring that the Washington Ocean Acidification Center is employing in Washington waters. The ecological, cultural, and economic assets of the Salish Sea are highly vulnerable to the effects of OA. Monitoring biological effects can help us understand and respond to likely impacts. Results of our monitoring reveal severe cases of shell dissolution across multiple locations in Puget Sound that strongly correspond with the intensity of OA conditions in the natural environment. Shell dissolution varies temporally and spatially, but patterns of dissolution are comparable in space and time and can be used to identify seasonally important drivers of OA and vulnerable hot spots. Long-term monitoring of shell dissolution can provide insights into how changes at the individual lead to population level effects. We conclude with a discussion of the use of shell dissolution as biological criterion for water quality assessment to support management actions

The impacts of upwelling, ocean acidification and respiration on aragonite saturation along the Washington continental margin

The continental shelf region off the Washington coast is seasonally exposed to water with a low aragonite saturation state by coastal upwelling of deep waters. However, the extent of its evolution in late summer has been largely unknown. Along this continental margin, upwelling, biological productivity, and respiration processes in subsurface waters are major contributors to the variability in aragonite saturation state. In the late summers of 2011 and 2012, we conducted large-scale chemical, biological, and hydrographic surveys of the region in order to better understand the interrelationships between these natural and human-induced processes and their effects on calcium carbonate saturation. The uptake of anthropogenic CO2 has caused the aragonite saturation horizon to shoal by approximately 40-50 m since preindustrial times so that it is well within the density layers that are currently being upwelled along the west coast of North America to depths between 10 and 80 m. Although the majority of the corrosive character of these waters is the result of respiration processes at intermediate depths, reducing aragonite saturation state by about 0.2-0.3 and pH by 0.3-0.5, this region continues to accumulate more anthropogenic CO2 and, therefore, the upwelling processes will expose coastal organisms living in the water column or at the sea floor to less saturated waters, exacerbating the biological impacts of ocean acidification. Our research shows this is happening now with some pteropod species

Vulnerability and Adaptation Strategies of Pteropods in the California Current Ecosystem

The ocean uptake of anthropogenic CO2 has shoaled the aragonite saturation horizon in the California Current Ecosystem, but only a few studies to date have demonstrated widespread biological impacts of ocean acidification under present-day conditions. Pteropods are especially important for their role in carbon flux and energy transfer in pelagic ecosystems. In the California Current Ecosystem, conditions are becoming increasing unfavorable for sustaining shell maintenance because of enhanced dissolution. Our results show a strong positive correlation between the proportion of pteropods with severe dissolution and the percentage of the water column that is undersaturated with respect to aragonite. From this relationship, we are able to determine the extent of dissolution for the pre-industrial era, 2011, and 2050. Our calculations show that dissolution has increased by 30% since the beginning of the industrial era, and could increase to 70% by 2050. Although dissolution is occurring in most of the investigated pteropod species, some species have changed their daily vertical distribution pattern by migrating to upper supersaturated waters to avoid corrosive waters, a potential indication of an adaptation strategy to ocean acidification