Projects
GAGE (Guianna Abbysal Gyre Experiment)
Principal Investigator
Michael McCartney
Project Description
The Hypothesis: There exists a western intensified cyclonic deep-recirculation gyre beneath the tropical and subtropical thermocline of the North Atlantic, the "Guiana Abyssal Gyre." This gyre causes the transport of the Deep Western Boundary Current to be more than double that of the net cold-water export in the meridional overturning circulation.
In summary, the foundation of the hypothesis of the Gyre rests on two strong cornerstones: the robust estimates of the primary MOC amplitude of order 15 Sv, and the DWBC amplitude larger than that by a factor of 2 or 3. Together these demand recirculation: that there be a large northward flow of cold water across the rest of the basin offshore of the DWBC at all latitudes where that large DWBC is observed, to partially compensate that large transport and reconcile the observed large DWBC and the MOC amplitude. The Gyre hypothesis is of a strong western intensification of that recirculation, and is built from the cornerstones by indirect evidence: geostrophic shear and water mass distributions. The proposed GAGE intends to provide a third cornerstone to the foundation of the Gyre hypothesis, the direct measurement of the recirculating flow: its existence and its intensity. READ MORE ...
VEX (Exploratory Moored Measurements in the Vema Fracture Zone)
Principal Investigator
Michael McCartney
Project Description
This project has the primary goal of measuring the magnitude and vertical and lateral structure of the eastward flow of bottom and deep waters through the Vema Fracture Zone (VFZ). This will establish mean values and intra-annual variabilities for a year long record, including transport distribution in temperature classes, at a location upstream of the primary sill, before the expected intense mixing at the sill blurs the distinction between bottom and deep waters. A secondary goal VEX is to estimate the intensity of the mixing that occurs between deep and bottom waters as they flow through the VFZ from heat and mass budgets of the measured bottom water flow and the disappearance of the coldest classes downstream along the VFZ. Exploratory measurements of the statistics of time series profiles of velocity shear and hydrography at the primary sill will independently provide estimates of the intense mixing regime through fine structure parameterizations, collaborative work with Kurt Polzin, WHOI. READ MORE ...
Southern Ocean Circumpolar Flows, Transformation, Recirculations and Intergyre Exchanges
Principal Investigators
Michael S. McCartney and Kathleen A. Donohue
Project Description
The traditional image of ocean circulation between Australia and Antarctica is of a dominant belt of eastward flow, the Antarctic Circumpolar Current, with comparatively weak adjacent westward flows that provide anticyclonic circulation north and cyclonic circulation south of the Antarctic Circumpolar Current. This image mostly follows from geostrophic estimates from hydrography using a bottom level of no motion for the eastward flow regime and typically yield transports near 170 Sv. Net eastward transport for this region of about 145 Sv results from subtracting those westward flows. This estimate is compatible with the canonical 134 Sv through Drake Passage with augmentation from Indonesian Throughflow (around 10 Sv). READ MORE...
Branches, Birfucations, and Retroflections over the Tail of the Grand Banks
Principal Investigators
Michael McCartney and Paula Fratantoni
Project Description
It is proposed to analyze existing data (hydrography, current meter, surface drifter, subsurface float, altimetric and SST observations), to characterize the mean and variable (mesoscale through seasonal to interannual) regional circulation around the Tail of the Grand Banks, ultimately enabling a more complete description of the branches, bifurcations and retroflections of the currents. This is a critical location for the North Atlantic circulation. There, major branches of the wind-driven (Gulf Stream and Labrador Current) and thermohaline circulations (Deep Western Boundary Current) meet, and dramatic changes in the character and pathways of the currents follow. The Labrador Current and Deep Western Boundary Current partially retroflect near the Tail of the Banks, but the amount of transport lost by the combined currents and the details of the retroflection pathway are unknown. Similarly, south of the Grand Banks, the Gulf Stream approaches the Tail from the west with full-depth flow carrying large transport. READ MORE...