NOAA  National Centers for Coastal Ocean Science. NCCOS

December 2021  New Study Unveils the Unique Seasonality in the Deep Basins of Gulf of Maine https://coastalscience.noaa.gov/news/new-study-unveils-the-unique-seasonality-in-the-deep-basins-of-gulf-of-maine/


Variability of Deep Water in Jordan Basin of the Gulf of Maine: Influence of Gulf Stream Warm Core Rings and the Nova Scotia Current
Jiabi Du, Weifeng G. Zhang, Yizhen Li
Published on: 12/02/2021
Primary Contact(s): yizhen.li@noaa.gov

Research Area(s): Coastal Change / Climate Impacts on Ecosystems; Stressor Impacts and Mitigation / Harmful Algal Bloom Detection and Forecasting
Region(s) of Study: Waterbodies / Gulf of Maine

Abstract
As the nutrient-rich subsurface slope water intruding into the deep basin of the Gulf of Maine (GoM) supports the high biological productivity in the semi-enclosed gulf, it is important to understand the process and time scale of such slope water intrusion. 

This study focuses on variations of the GoM deep water on seasonal to interannual time scales and the influences of open ocean processes on the temporal variation of the deep water properties. 

Based on long-term monitoring data, it is found that the deep water at Jordan Basin (one of three major basins in the GoM) is persistently warmer in winter than in summer, which is distinctly different from the seasonality of surface water in the basin and the deep water on neighboring shelf seas. The unique seasonality in the deep GoM reflects a time-lagged response to shoreward intrusion of the subsurface slope water off the GoM. 

Both observation-based lag-correlation analyses and numerical simulations confirm a timescale of approximately 3 months for the intruding subsurface slope water to flow from Northeast Channel to Jordan Basin. 

Properties of the intruding slope water at the Northeast Channel were significantly correlated with the Gulf Stream position and dramatically impacted by episodic warm-core rings shed from Gulf Stream.

Inside the deep GoM, the intruding slope water was also indirectly affected by the fresher water input from Nova Scotia Current. Spreading of the fresher water inside the gulf strengthens near-surface stratification, suppresses deep convection, and preserves heat and salt in the deep GoM during the wintertime.

Key Points

Bottom water temperature at Jordan Basin is warmer during winter than summer, which is distinctly different from neighboring shelf seas

This unique seasonality reflects a delayed response (approximately 3 months) of Jordan Basin to the changes in the slope sea

Deep water at Jordan Basin is affected by the Nova Scotia Current and Gulf Stream warm-core rings


Plain Language Summary
Nutrient-rich slope water intruding into the deep basin of the Gulf of Maine  provides 30% of the nutrients needed to support the high biological productivity and high yield fisheries in the gulf. 

Our analysis of long-term mooring data shows that the deep water in the Gulf of Maine changes in a unique fashion: being warmer in winter and colder in summer. 

This unique seasonality differs dramatically from the deep water on the neighboring continental shelves. 

It represents a delayed response of the deep water in the gulf to seasonal changes of the major currents in the adjacent open ocean. 

We explained the timescale of this delayed response from multiple angles using mooring data, numerical simulations, and remote sensing data. We found that signal of open ocean change at shelf edge (e.g., induced by Gulf Stream meandering and associated eddies) propagates into the deep gulf basin in about 3 months. 

Meanwhile, the surface buoyant and low-salinity inflow from the upstream Scotian Shelf into the Gulf of Maine tends to suppress vertical mixing in the gulf and helps maintain the heat and salt stored in the deep gulf; even in the wintertime when the surface ocean loses heat to the cold atmosphere.