Title

Changes in the Arctic and their impact on the oceanic meridional overturning circulation

Date of Award

2001

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Meteorology and Physical Oceanography

First Committee Member

Claes G. H. Rooth, Committee Chair

Abstract

Variations of the sea ice condition in the Arctic and its adjacent seas could significantly influence the earth's climate. Recent observations show that both sea ice and oceanic properties in the polar and sub-polar seas are undergoing significant changes. In this study, by applying a coupled sea ice-ocean model---the Miami Isopycnic Coordinate Ocean Model and the elastic-viscous-plastic dynamic-thermodynamic sea ice model and the NCEP/NCAR reanalysis data, the changes of the Arctic sea ice caused by the NAO-related atmospheric anomalies and the response of the oceanic Meridional Overturning Circulation (MOC) to these changes are investigated.Model solutions indicate that the Arctic sea ice varies with the atmospheric transients. The summer minimum sea ice extent in the high NAO case reduces about 17% of that in the low NAO case. The largest reduction in multi-year ice extent is along the Siberian coast region. Horizontally, ice is about 1 to 2 m thicker (thinner) at Eurasian coast (Canadian) side of the Arctic in low NAO years relative to that in high NAO years.Sea ice export from Arctic through Fram Strait is about 5474 km 3 per year in high NAO years, more than doubled of that in low NAO years. This high efflux is mainly caused by the increased strength of the wind forcing. The rate of the net sea ice production in the high NAO case is about 10 times as that in the low NAO case along the Siberian and Alaskan coasts, and 2 to 3 times in the other regions. The high rate of ice production is related to the efficient sea ice transport and the low ice compactness. It is worth mentioning that in the model solution, a net sea ice influx from the Barents Sea to the Arctic basin makes up 15 to 18% of the ice efflux at Fram Strait. The ice efflux at Fram Strait follows the NAO transients without any noticeable time lag.The strength of the MOC is 16.2, 13.4 and 12.3 Sv in the high NAO, climatic and low NAO cases, respectively. The rate of dense water formation in the high NAO case is about 3 Sv higher than that in the low NAO case in the Labrador Sea and south of the Denmark Strait region, and 1 Sv weaker in the Greenland Sea. The overall dense water formation is almost the same in the ice related marginal seas. Model solutions also show that the longterm persistent atmospheric anomalies are important for generating systematic MOC variations. MOC also responds quickly to the decadal timescale atmospheric fluctuations. Because the adjustment timescale of the MOC is long, the response of the MOC to the NAO transients is sensitive to the initial state of the forcing fields.

Keywords

Physical Oceanography

Link to Full Text

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