Enhancement of Particle and Carbon flux studies at Station W

Tim Eglinton, Marine Chemistry & Geochemistry

OCCI Funded Project: 2006

Proposed Research

The production, recycling and burial of organic matter over the ocean margins represents a key component of the global carbon cycle.  Understanding the processes governing carbon cycling on the margins is of particular relevance in relation to questions concerning the ocean’s capacity to absorb carbon dioxide from the atmosphere. One aspect that is not well understood concerns the exchange of carbon between the ocean margins and the deep sea.  This process exerts an important constraint on the ability of the oceans to sequester and act as a sink for CO2.

In order to address this question, we previously secured funds from the National Science Foundation to study carbon cycling over the New England margin.  This location is influenced by the Deep Western Boundary Current (DWBC) which runs parallel to the slope, and we have hypothesized that this current transports and redistributes particulate organic matter over the margin and serves as a conduit for carbon export to the deep sea. We speculate that past (and future) climate-driven changes in the DWBC could influence the distribution and extent of carbon burial in this important region.  The project involves the collection and characterization of organic matter associated with sinking and suspended particles.  Efforts thus far have been focused at a site in approximately 3000 m of water on the continental slope where a mooring has been deployed with sediment traps to intercept particles raining to the sea floor.  Although preliminary results have revealed the existence of significant lateral movement of carbon as originally hypothesized, the design of our program does not allow us to differentiate between along-slope versus down-slope carbon transport. 

Through Ocean & Climate Change Institute funds from the Comer Foundation, we have built upon the above program with the purpose of better defining carbon transport over the New England margin.  Specifically, these funds have supported the deployment of a second sediment trap mooring, T-2, upslope (in 2000 m of water) from our existing mooring (Figure 1).  With this configuration, we can separately identify and quantify the different pathways of carbon and develop an accurate picture of carbon cycling in this dynamic oceanic setting.  Most importantly, simultaneous interception of particles by near-bottom traps at these two different locations on the slope will allow us to constrain the trajectory and overall importance of near-bottom transport in dictating the fate of organic carbon produced over the margin. 

During the first part of the year, the various components of the new mooring were assembled.  The mooring was then deployed on a research cruise aboard R/V Oceanus in June, 2006 (Figure 2).  The mooring consists of three sediment traps - one at 1000 m, another at 1500 m and the third 50 meters above the sea floor.  The traps enable particles to be collected in up to 23 time-windows over the course of a year-long deployment (i.e., representing 2-3 week time intervals) in order to capture seasonal variability.  We will recover the mooring and sediment traps in June 2007 and will immediately begin processing these samples for geochemical characterization.
The data emanating from this study will provide synoptic measurements on the rate of supply and composition particles collected at two locations at different depths on the continental slope. In this way we will be able to build a detailed picture of carbon export in this productive and dynamic region of the North Atlantic Ocean.