Collaborative Research: Ocean Pressure in the Arctic Derived From Satellite Gravity Observations and In Situ Pressure Measurements

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The research will estimate the large-scale seasonal and longer time variations in the Arctic Ocean bottom pressure, sea level, and circulation using in-situ observations of deep- sea pressure, hydrographic and atmospheric data, and satellite gravity. Sea level in the central Arctic Ocean is a crucial determinant of the ocean's circulation, and as such it strongly affects the sea-ice distribution and the regional freshwater budget. Climate variability is linked to changes in albedo associated with changes in sea-ice distribution and to changes in the global thermohaline circulation associated with changes in the export of Arctic Ocean freshwater and sea ice. Observing the pressure distribution in the ocean is thus central to understanding the variability in the ocean circulation. Current perspectives of the ice and freshwater distribution and their variations are based on available hydrographic surveys and measurements from a few automated instruments. The lack of routine, spatially continuous measurements of the freshwater distribution makes it difficult to construct a complete picture of frontal locations at any one time. The scientific goal and merit of this work is to improve indices of ocean change related to climate variability and to contribute to achieving the goal of obtaining systematic measurements of large-scale ocean circulation and freshwater distribution from space. Bottom pressure recorders (BPRs) will be deployed in a 100 km triangular array with vertices at the Pole, the Lomonosov Ridge, and near the foot of the ridge. These in situ measurements will be compared with GRACE (the Gravity Recovery and Climate Experiment satellite mission) estimates of deep-sea bottom pressure in the central Arctic Ocean to cross- validate these methods of pressure retrieval. BPRs also provide measurements of tides and other short period ( 60 days) variability, and will be used to reduce aliasing problems in the satellite measurements. GRACE time-dependent bottom pressure fields for the whole basin will be compared with measured bottom pressure, coastal sea level records, and hydrographic data to estimate ocean circulation changes and thereby evaluate the accuracy of the combined remote sensing, in situ measurement approach. This work will contribute to the long-term goal of comparing remote sensing measurements of bottom pressure with satellite altimeter observations of sea surface height to produce not only estimates of circulation changes but also estimates of the total steric anomaly and inferred fresh water and sea ice content. Results from this work include in situ BPR records, derived tidal constituents, drift corrections, the drift corrected pressure with tides removed, and the spatial field of bottom pressure estimates from GRACE after tide removal. These will be archived in the ARCSS and SEARCH data banks and supplied directly to those collaborating on the system of Arctic Ocean sea-level observations. For broader dissemination, pressure-derived sea-level gradient and barotropic transport estimates will made available on the Web as well as archived in the ARCSS and SEARCH data banks. This project will establish collaborations between three institutions: the Universities of Washington and Colorado, and the Jet Propulsion Laboratory, and will require expertise in several disciplines: oceanography, geodesy, and solid earth geophysics. The work, which will form the PhD thesis project of a University of Washington graduate student and part of the PhD project of a University of Colorado graduate student, will be a first step towards integrating time-variable satellite gravity observations into physical oceanography. These observations constitute a new and innovative data type for oceanography, with considerable promise for improved and broader understanding of the circulation of the polar and global oceans.