The Winter Transatlantic OACES Section along 24N

The Intergovernmental Panel of Climate Change states that two of the largest uncertainties in the current predictions of climate change include the sources and sinks of greenhouse gases like carbon dioxide and the role of the ocean in mitigating or changing the timing and regional patterns associated with a warmer climate. Part of the uncertainty in the sink of carbon is the extent to which the Atlantic ocean sequestors carbon and exports it to other ocean basins through the meridional overturning circulation. To quantify the inventories and fluxes of carbon within the worlds oceans and complete the world survey measurements will be required along the 24N transatlantic line.

Hydrographic and velocity measurements collected will quantify the water masses and determine the meridional overturning circulation responsible for the redistribution of carbon in the center of the subtropical gyre and estimate the remineralization component of the CO2 increase in order to quantify the anthropogenic CO2 burden. To determine the flux of carbon, the mesoscale structure of ocean currents will need to be resolved. Full water column, basin wide measurements with direct velocities will be necessary to determine the circulation central to estimating the carbon flux across 24N.

In addition to this primary goal, these measurements will also allow a relatively rich scientific inquiry due to the location and timing of this section, and the wide range of existing historical data sets in the region. The 24N transatlantic section has been previously occupied in 1957, 1981, and 1992, revealing long-term variability in mid-depth temperature, salinity, and oxygen. The new data set will extend this time-series through a time when relatively large mid-depth changes due to decadal variations in the air-sea interaction for Labrador Sea Water formation have been already been observed. In addition, this winter cruise will complement those in the other seasons to allow for investigation into seasonal variations in fluxes of mass, heat, and freshwater. This data will thus prove a valuable scientific component to other programs such as NSF/Clivar and NOAA/ACCP, whose goals include determining the magnitude of the meridional overturning circulation during the field phase of ACCE.

Hydrographic and velocity data will be analyzed to quantify the flux of carbon as well as to (1) determine the intensity and characteristics of the meridional overturning circulation; (2) assess the decadal changes in deep water masses by comparing with previous surveys; and (3) quantify the heat and fresh water fluxes across the center of the subtropical gyre. Hull mounted acoustic doppler current profiler and lowered acoustic doppler current profiler (LADCP) data will be analyzed (1) to compute directly meridional heat flux and compare the results to the geostrophic estimate; (2) to estimate ageostrophic currents and help to determine Ekman transports; and (3) to compare these LADCP results with other direct velocity estimates along the same transect and ascertain the robustness of various barotropic signals.