Investigating Mid-Atlantic Cold Pool Dynamics: The Ocean Glider Component

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W.S. Brown, C. Jakubiak, & R. Arena

OCEAN Observation Laboratory (OCEANOL)
School for Marine Science and Technology (SMAST)
University of Massachusetts at Dartmouth
New Bedford, MA

Program Goal: Measurement of the hourly-seasonal/1km-100km features of the Mid-Atlantic Cold Pool

To do this, we will employ a joint observation/modeling program focused on the Middle Atlantic Bight (MAB)/Southern New England Bight (SNEB) regions of the continental shelf between Cape Cod to Cape Hatteras (Figure 1). We plan focus ocean glider measurements on the seasonal evolution of the Cold Pool from its winter origins near the end of March, through its formation due to the onset of near-surface stratification in late May 2012, through its summer maintenance phase, to its September/October demise due to the strong vertical mixing associated with autumn storms. Numerical circulation models will be assimilating many of the measurements and producing Cold Pool maps throughout the field season.

The 2012 field season: The primary measurements of the Cold Pool and related biology will be opportunistic glider-borne measurements of temperature (T), salinity (S), oxygen (O), optical backscatter (OB), and estimated velocity (V). T, S, and V will be assimilated into one or more of the existing Mid Atlantic Regional Association Coastal Ocean Observing System (MARACOOS) circulation models which will provide 4-D maps of the Cold Pool evolution. The demonstration Cold Pool project will benefit from other ongoing measurements, including MARACOOS (a) high frequency (HF)-derived maps of surface current; (b) satellite SST and color maps; (c) weekly Oleander cross-shelf transect TSV measurements; (d) the NOAA Northeast Fisheries Science Center (NEFSC) regional surveys of fish, plankton, and water properties; and (e) possibly repeat glider measurements of the Ocean Observation Initiative (OOI)-Pioneer Array region.

Deployment I: Early April 2012          ….to define MAB Winter 2012 water

Deployment II: Late May 2012           ….to define 2012 Cold Pool water

Deployment III: Late August 2012      ….to define modified Cold Pool water

Deployment IV: Mid-October 2012    ….to define the demise of Cold Pool water

The gliders flying @ 26km/day take about 4 weeks to traverse from Martha’s Vineyard to New Jersey via the Pioneer Array region. Its flight will be aided by the estimated ~ 5 km/day (5 cm/s) westward alongshelf advection in the MAB/SNEB. The glider missions will be guided by the MARACOOS Glider Technical Center - a network including a central node at Rutgers University and secondary nodes at UMass Dartmouth and UMaryland–Horn Point.

Figure 1Figure 1. The MARACOOS Northeast Domain Glider BLUE’s 1-13 April 2012 Mission-I schematic trajectory (thick dashed). BLUE’s planned May 2012 Mission-II will be a MA–NJ transect (thin black line). The color-coded bathymetry contours are at 10m intervals between the coast and 200m depth.

Deployment-I: 1-13 April 2012       

Glider BLUE was deployed using the SMAST RV Lucky Lady (berthed in Fairhaven, MA) at a site west of Gay Head Martha’s Vineyard V [41o 16.2427’N; 71o 00.1500’W] on 1 April 2012. We programmed her to execute a triangular (1 km on a side) test mission. With crucial assistance from Chip Haldeman and Dave Aragon we checked out BLUE’s performance before sending it toward New Jersey via a corner of the OOI Pioneer Glider Survey domain. Unfortunately, the compass failed and we had to return BLUE to its original deployment site where it was recovered on 13 April 2012. Still BLUE covered 225 km in the 13 days and provided a nearly complete data set – the contoured temperature transect is shown in Figure 2.

Deployment-II: Late May 2012       

We plan to deploy glider BLUE in late May to profile the Cold Poll 2012 during Mission-II: a flight leaving from just west of  Martha’s Vineyard (MV) and heading toward the western corner of the OOI Pioneer array glider domain; and then on to New Jersey. (see the zig-zag mission plan in Figure 1).

Figure 2Figure 2. The 1-13 April 2012 glider BLUE temperature transect in the Southern New England Bight (SNEB). The dashed bars define the section of focus in section A of this report.