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Ocean Acidification

Horizontal and Vertical Distribution of Thecosome Pteropods in Relation to Carbonate Chemistry in the Northwet Atlantic and Northeast Pacific
The impact of ocean acidification on marine ecosystems represents a vital question facing both marine scientists and managers of ocean resources. Thecosome pteropods are a group of calcareous planktonic molluscs widely distributed in coastal and open ocean pelagic ecosystems of the world’s oceans. These animals secrete an aragonite shell, and thus are highly sensitive to ocean acidification due to the water column’s changing carbonate chemistry, and particularly the shoaling of the aragonite compensation depth at which seawater becomes corrosive to aragonite. In many regions, however, relatively little is known about the abundance, distribution, vertical migratory behavior, and ecological importance of pteropods. Assessing the likely ecosystem consequences of changes in pteropod dynamics resulting from ocean acidification will require a detailed understanding of pteropod distribution and abundance relative to changing aragonite saturation in the water column.

The primary objective of this project is to quantify the distribution, abundance, species composition, shell condition, and vertical migratory behavior of oceanic thecosome pteropods in the northwest Atlantic and northeast Pacific, and correlate these quantities to hydrography and concurrent measurements of carbonate chemistry, including vertical and horizontal distributions of aragonite saturation. In particular, the project will capitalize on present-day variability in the depth distribution of aragonite saturation levels within and between the Atlantic and Pacific Oceans as a ‘natural experiment’ to address the hypotheses that pteropod vertical distribution, species composition, and abundance vary as the compensation depth becomes shallower. Secondary objectives are to develop acoustic protocols for the remote quantification of pteropod abundance for future integration into ocean acidification monitoring networks, and to characterize carbonate chemistry and nutrients along portions of two WOCE/CLIVAR Repeat Hydrography transects (A20 in the Atlantic and P17N in the Pacific) to identify decadal-scale changes in the carbonate system. These hypotheses and objectives will be addressed through two cruises along survey transects between 35 and 50°N in the northwest Atlantic and northeast Pacific involving a combination of station-work and underway measurements, and a comprehensive array of instruments, including acoustic, optical, net, hydrographic, and carbonate chemistry sensors.

In-Situ Carbon Sensors

In-Situ Carbon Sensors
The marine CO2 (carbonate or inorganic carbon) system, represented by four primary parameters – partial pressure of CO2 (pCO2) or CO2 fugacity (fCO2), total dissolved inorganic carbon (DIC or TCO2), pH, and total alkalinity (AT), is central to the marine carbon cycle, which plays a critical role in regulating the world’s oceans as CO2 sinks or sources to the atmospheric reservoir. Study of this system is critical to understanding its dynamics. In addition, investigation of δ13C variability in the world’s oceans can provide valuable insight as to the provenance, magnitude, transport and eventual fate of CO2inputs.

The aim of the project is to develop and deploy a buoy-based technology for long-term measurement of the seawater CO2 system (pH and total inorganic carbon or DIC) and inorganic carbon isotopic composition in subsurface marine environments. We focus our in-situ sensor development to achieve high-frequency, concurrent measurement with sufficient long-term accuracy for use in climate studies. The pH and DIC measurements will be based on spectrophotometric principles using pH sensitive indicators, and carbon isotopic measurements will be made by underwater isotope ratio mass spectrometry (IRMS). Our design strategy involves use of low power components and minimization of reagent volumes. Measurement will be achieved without sacrificing sensitivity available with the existing instruments. This integrated sensor package will also provide connectivity to various commercially available peripheral sensors, including an in-situ O2 optode and CTD.

Simultaneous measurement of pH and DIC allow the seawater CO2 system to be fully characterized via thermodynamic calculation with minimal error. Integration of this bulk CO2 measurement with δ13C CO2 isotopic analysis is not only a fundamental advancement in in-situ chemical sensing technology, but will also provide a means of obtaining valuable information such as origin, distribution, dynamics, biogeochemical role, and eventual fate of CO2 within marine ecosystems. This technology is well aligned with the implementation goals of the on-going Ocean Observatories Initiative (OOI).

Towards Long-term Monitoring of the CO2 System in Arctic Rivers

The CO2 systems (pH, pCO2, DIC, and TAlk) in rivers and their estuaries play a critical role in regulating inorganic carbon, including CO2, fluxes into and out of the systems, and yet they have been understudied in the past. Currently, we don’t have a clear understanding of how much this system contributes to global CO2 budget, and can not make reasonable projection on how its fate is going to be under rising atmospheric CO2 concentration that primarily drives global climate change. Previous measurements of the CO2 systems in Arctic rivers and their estuaries are not complete and much less precise than most of seawater measurements. We thus lack of information on their long-term trend and short-term variation, which are essential to predict how they response to apparently accelerated climate change in Arctic region.

The Arctic Ocean receives large amount of riverine fluxes of organic matter, suspended material, and nutrients from surrounding rivers, and the riverine influence is most substantial among all ocean basins. Arctic region is also most sensitive to global climate change. The CO2 systems in Arctic rivers and their estuaries would likely undergo a significant and observable change in a relatively shorter time scale (50 – 100 years). Increase in riverine inorganic carbon fluxes is expected as warming climate may accelerate water cycle and weathering processes. This increase of inorganic carbon load may have significant impacts on riverine and coastal carbon cycles, and their associated ecosystem functioning. The already observed increase of riverine organic carbon flux in Arctic may also enhance microbial respiration and organic carbon degradation, both of which would drive the CO2 level in water towards over-saturation, thus release more CO2 to the atmosphere. To study these potential changes in Arctic rivers, both long-term and short-term measurements are required.

This project aims to initialize a time-series measurements of the CO2 system in Mackenzie River, one of the major Arctic river in North America. The field campaign include both diurnal and monthly sampling of all major CO2 system parameters in river water, and all measurements will be performed by state-of-art instruments to obtain high precision and accuracy as required by the research. This work will serve as the initial step towards long-term measurements and studies of impacts of global warming on the CO2 systems in Arctic rivers, their estuaries, and adjacent coastal waters.

Global River Biogeochemistry

The CO2 systems lab collaborates with the Global Rivers observatory project to better understand how river systems contribute to the global inorganic carbon budget. This project seeks to characterize the sources, pathways and timescales of riverine export of organic and inorganic carbon from land to the ocean. Follow the link to to read more about this project.

Coastal Carbon Cycle

In this project, we investigate the dynamic tidal export of dissolved inorganic carbon (DIC) to the coastal ocean from highly productive intertidal marshes and its effects on seawater carbonate chemistry. We combine high resolution in-situ measurments with marsh water samples of CO2 parameters and high-resolution intertidal salt marsh modling to characterize the complex export of DIC and alkalinity from marshes.


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Last updated October 24, 2016
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