Links between changes in the Hadley Circulation and Oceanic Oxygen Minimum Zones

Thursday, July 30, 2015: 2:00 PM
Gabriela De La Cruz Tello, San Jose State University, San Jose, CA, United States, Caroline Ummenhofer, Woods Hole Oceanographic Institution, Woods Hole, MA, United States and Kristopher B Karnauskas, Woods Hole Oceanographic Inst, Woods Hole, MA, United States
Abstract:
Recent research argued that the Hadley circulation (HC) is composed of three regional cells located at the eastern edges of the ocean basins, rather than a single, globe-encircling cell as the classic textbook view suggests. The HC is expected to expand in concert with global warming, which means that the dry regions beneath the descending branches of the HC are projected to become even drier. Changes in the HC are thus likely to impact freshwater resources on land, as well as the underlying ocean in the subtropics. The eastern edges of ocean basins are characterized by oxygen minimum zones (OMZs), which are regions of very low oxygen concentrations. Near the surface, sunlight causes oxygen to decline via microbial respiration. In areas where the rate of production at the surface is increased and ventilation is low, this process results in OMZs. They affect marine life, as many animals cannot handle the stress caused by such conditions. OMZs have expanded and shoaled in the last 50 years, and they are expected to continue to do so as global climate changes.

The purpose of this research is to find links between the projected changes in OMZs and the HC. The National Center for Atmospheric Research (NCAR) Community Earth System Model 1.0 (CESM), Representative Concentration Pathways 8.5 (RCP8.5) experiment with a resolution of 0.9 by 1.25 degrees, which formed part of the Coupled Model Intercomparison Project phase 5 (CMIP5), was used for this analysis. Meridional winds and oceanic oxygen concentrations were the primarily analyzed variables. Latitudinal ocean oxygen slices demonstrate the OMZs’ location along the eastern edges of ocean basins. Meridional winds overlayed with oxygen concentration are consistent with the idea that surface meridional ‘Hadleywise flow’ (i.e., towards the equator at the surface and towards the poles aloft) and OMZs are linked through changes in upwelling. Area-averaged time series spanning the historical period through to the end of the 21st century with RCP8.5 confirm that future changes in OMZs and the HC may be connected. Additional analyses of upwelling characteristics and variations in ventilation could lead to improved understanding of the factors that drive these OMZ changes.

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