Dynamics and spatio-temporal variability of the Mid-Atlantic Bight Cold Pool

The Mid-Atlantic Bight (MAB) Cold Pool is a bottom-trapped cold (lower than 10 °C) and fresh (lower than 34 psu) water mass, that is isolated from the surface by the seasonal thermocline, and is located over the mid- and outer-shelf of the MAB. It has been recognized that the Cold Pool plays an important role in impacting the along-shelf and across-shelf seasonal and interannual variations of temperature, salinity, sea surface slope, and exchange of heat and salt. Environmentally driven changes in habitats, have been shown to have a first order impact on the MAB ecosystem. For example, spatio-temporal variability of the Cold Pool exerts strong influence on the recruitment and settlement of several cold-temperatures fish species in the MAB ecosystem. Following the Cold Pool definition, we put forward a method that includes three criteria to capture and quantify the Cold Pool characteristics, based on a 50-year (1958-2007) high-resolution regional ocean model hindcast simulation. The seasonal climatology of the Cold Pool and its properties are investigated during its onset - peak - decline cycle. Three stages of the Cold Pool event are defined according to its evolving status and characteristics. The cores of the Cold Pool usually travel along the 60-m isobath starting south of the New England shelf to the Hudson Shelf Valley at a speed of approximately 2 cm/s. The depth-averaged heat budget of the near-bottom water column (below 30-m depth) over the MAB and Georges Bank is investigated to compare the relative contribution between the vertical diffusion from the surface layer and advection during strong and weak Cold Pool years. Possible origins of the Cold Pool are investigated by performing a lead-lag correlation analysis. Results suggest that the Cold Pool originates not only from local remnants of winter water near the Nantucket Shoals, but has an upstream source traveling in the spring time from the southwestern flank of the GB along the 80-m isobath. The interannual variability of the Cold Pool and summer progressions are also investigated. Results show that the Cold Pool exhibits significant year-to-year variability in the state variables (persistence time, volume and temperature), spatial distribution and the equatorward progression. Based on the persistence time, volume and volume-averaged temperature, a Cold Pool Index (CPI) is defined and computed in order to represent the strength of the Cold Pool. Anomalous strong and weak years are investigated using a composite analysis according to the CPI values. The volume-averaged heat budget of the Cold Pool region between strong and weak years is investigated. Results suggest that abnormal warming/cooling from initial temperature and horizontal advection drives the interannual variability in temperature. The depth-averaged temperature anomaly in the Cold Pool region is largely determined by the initial temperature anomaly in the early spring, suggesting a potential for seasonal predictability. Statistical relationships between the Cold Pool temperature and large-scale oceanic and atmospheric processes in the Northwest Atlantic Ocean are investigated. The relationship between the Cold Pool temperature and the north-south shift of the Gulf Stream position are investigated. Results shows that the spring Cold Pool temperature has a significant positive correlation with the annual Gulf Stream index. Besides, the fall Gulf Stream position is significantly correlated with the Cold Pool temperature in the following spring, enhancing the use of the fall Gulf Stream position as a leading indicator of the Cold Pool temperature. The Cold Pool temperature also has a positive response to the winter NAO, with the Cold Pool temperature lagging the NAO by approximately 2 years. The possible mechanistic link between the Cold Pool temperature, Gulf Stream position and the NAO are discussed.Ph.D.Includes bibliographical referencesby Zhuomin Che