Seasonal warming of the Middle A tlantic B ight C old P ool

Abstract

The Cold Pool is a 20–60 m thick band of cold, near‐bottom water that persists from spring to fall over the midshelf and outer shelf of the Middle Atlantic Bight (MAB) and Southern Flank of Georges Bank. The Cold Pool is remnant winter water bounded above by the seasonal thermocline and offshore by warmer slope water. Historical temperature profiles are used to characterize the average annual evolution and spatial structure of the Cold Pool. The Cold Pool gradually warms from spring to summer at a rate of order 1°C month−1. The warming rate is faster in shallower water where the Cold Pool is thinner, consistent with a vertical turbulent heat flux from the thermocline to the Cold Pool. The Cold Pool warming rate also varies along the shelf; it is larger over Georges Bank and smaller in the southern MAB. The mean turbulent diffusivities at the top of the Cold Pool, estimated from the spring to summer mean heat balance, are an order of magnitude larger over Georges Bank than in the southern MAB, consistent with much stronger tidal mixing over Georges Bank than in the southern MAB. The stronger tidal mixing causes the Cold Pool to warm more rapidly over Georges Bank and the eastern New England shelf than in the New York Bight or southern MAB. Consequently, the coldest Cold Pool water is located in the New York Bight from late spring to summer.

Seasonal Variability of the Cold Pool Over the Mid‐Atlantic Bight Continental Shelf

“…The southern cold water source is quickly warmed and its southward traveling path is hard to identify south of the HSV. However, for the northern cold source, the Cold Pool cores move southward, with warming rates about 0.04 °C/day during Stage I and 0.03 °C/day during Stages II and III, which is consistent with values reported in Houghton et al () and Lentz (; about 1 °C/month). Following these Cold Pool cores, we can track the coldest water patch traveling down the shelf for the duration of the Cold Pool event.…”

“…Based on previous studies (Brown et al, ; Fairbanks, ; Houghton et al, ; Lentz, ), the Cold Pool is considered as a relatively cold and fresh water mass cooler than 10 °C located over the middle and outer shelf of the MAB below the seasonal thermocline during stratified season. Following this definition, three criteria are applied simultaneously to capture and quantify the Cold Pool: Temperature and Salinity Criteria: The temperature of the Cold Pool is defined to be lower than 10 °C (Houghton et al, ; Fairbanks, ; Brown et al, ; Lentz, ). Because of the tendency of the model to be slightly warm biased, we also explore the 11 and 12 °C as temperature criteria for the Cold Pool.…”

“…Temperature and Salinity Criteria: The temperature of the Cold Pool is defined to be lower than 10 °C (Houghton et al, ; Fairbanks, ; Brown et al, ; Lentz, ). Because of the tendency of the model to be slightly warm biased, we also explore the 11 and 12 °C as temperature criteria for the Cold Pool.…”

“…It has been recognized that the Cold Pool plays an important role in impacting seasonal variations of temperature, salinity, sea surface slope, nutrient fluxes and distributions over the MAB (Lentz, ; Sha et al, ). Environmentally driven changes in habitats have been shown to have a first order impact on the MAB ecosystem (Benway & Jossi, ; Narváez et al, ).…”

“…Lentz () explores the seasonal warming of the Cold Pool using in situ measurements of temperature and salinity profiles collected between 1955 and 2014. The average annual evolution and spatial structure of the Cold Pool were characterized, and he found that the warming rate of the Cold Pool is not spatially uniform, but rather warms more rapidly over GB relative to the rest of the MAB.…”