LMG 14-11: Cruise Report - ChinStrAP: Changes in Stratification at the Antarctic Peninsula

Abstract

The goal of the ChinStrAP (Changes in Stratification at the Antarctic Peninsula) project is to assess the role of mesoscale and submesoscale variability on water mass transformation and exchange across the continental shelf and slope in southern Drake Passage. Specifically we plan to: 1. Assess the influence of flow-topography interactions on the frequency and characteristics of mesoscale eddy generation along the southern boundary of the ACC. We will be sampling a region where the strong southern ACC front (SACCF) and the ACC's southern boundary run along the continental slope before interacting with the Shackleton Fracture Zone (SFZ) and deflecting northward. This is a known region of eddy generation, as observed from remotely-sensed sea surface height (SSH), sea surface temperature (SST) and ocean color observations. We hope to obtain the in situ observations necessary to determine the mechanisms by which these eddies are formed and how they contribute to cross-shelf exchange. 2. Explore the interactions between surface wind and buoyancy forcing on mixed layer depth variability and its implications for ventilation of the deep ocean. Southern Drake Passage is a key location where deep isopycnals rise towards the surface across the ACC and outcrop allowing direct exchange with atmospheric temperatures and gases. This process is critical to the equilibration of dissolved gas concentrations with atmospheric values and thus influences large-scale characteristics of Earth's climate. A large number of recent studies have pointed to the strong influence of submesoscale processes, both due to surface forcing and stirring by mesoscale eddies, on rapid changes in mixed layer depth. These changes come about through dynamic instabilities related to lateral gradients in mixed layer properties. The ACC is a location where strong lateral fronts align with strong westerly winds. This situation is similar to western boundary currents, however the internal density structure is considerably different in the ACC. Our measurement strategy should allow us to capture the evolution of these dynamical processes. 3. Carry out an XBT/XCTD transect across Drake Passage on the southbound leg as a contribution to Scripps High Resolution XBT/XCTD observing line (WOCE AX22). This information will provide larger-scale context for the data collected from the three gliders. 4. Determine with high spatially- and temporally-resolved measurements the characteristic internal variability in this regional current system. This work will help to better interpret long-term observations in this same location (e.g., LTER monitoring, the AX22 high resolution XBT/XCTD line). The observations will also help validate high frequency variability in numerical models as they push towards resolving key dynamical processes at the continental shelf break.

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