Project Summary

Ken Brink, James Irish, Robert Beardsley, Richard Limeburner

U.S. GLOBEC: Long-term ADCP, Moored and Lagrangian Measurements and
Analysis as part of the Georges Bank Study

I. Introduction:

The GLOBEC Georges Bank field study concludes in late 1999. As part of this effort, we will have collected (under Phase 2 funds already granted) five years worth of physical measurements involving moored observations, drifters and shipboard ADCPs (Acoustic Doppler Current Profilers). The main part of this proposal is to cover analysis of this large data set. We seek to use moored measurements to characterize the water properties (flow, hydrographic and biological) and important driving agencies. We seek to use drifters to understand dispersion, residence times and frontal processes. We propose to use historical hydrographic data to understand the historical representativeness of the GBS field period. We will use ADCP data to characterize Bank-wide flow patterns and their seasonal evolution. Finally, we desire to use our physical knowledge base to help answer interdisciplinary questions about how physical processes (which might be somewhat predictable through climate models) influence variations in biological recruitment.

II. Proposed Research:

We propose to carry out work in several directions, each treated individually below. Although the tasks are listed separately, the reader should realize that there is some artificiality in the separations, and that all personnel will work together to some extent. For example, moored current measurements provide useful context and supplements for the drifter and ADCP programs.

A. Telemetry from 1999 Moorings (Irish, leader)

As part of the Long-Term Moored Program, both GOES and ARGOS telemetry are utilized to return data daily to WHOI. In the 1999 field year, Beardsley and co-workers are proposing separately a Northeast Channel crossover experiment where knowledge that water from the Scotian Shelf has reached Georges Bank would trigger a rapid response survey. Much of the software for this effort is in place, and setting up the system should require minimal effort. The real-time data will also be accessible to other GLOBEC investigators.

B. Analysis of Moored Array Data (Brink, Beardsley, leaders)

The funds currently requested will cover the cost of editing, processing and archiving the results from the last (1999) mooring deployment. This will lead to the availability (to GBS investigators) of a five-year moored array data set on the web which will be supplemented by relevant sea level, air pressure and wind records from around the Gulf of Maine and along the Scotian shelf. Some scientific analysis of the existing moored array data set (1994--1996) is presently underway. These efforts tend to involve special events, or other problems that do not require (or are not better done) with a five-year time series.

When 2000 arrives, we will have a rather complete, 4--5-year set of time series at the Northeast Peak and South Flank locations, along with supplemental data. At this point, analyses can begin that involve maximal statistical confidence or ability to compare among years. Broadly speaking, these analyses can be divided into physical and interdisciplinary approaches, but all analyses will contribute to the overall GBS goal.

The purely physical analyses can be summarized as follows.

The extensive moored optical data set provides an opportunity for interdisciplinary analysis. The transmissometers and fluorometers can provide estimates of phytoplankton standing stock. This stock time series, in turn, can be used to relate any surges of productivity to spring restratification, upwelling events, or interactions of Bank waters with warm core rings. Thus, there is an opportunity to use correlative approaches to estimate what physical phenomena affect primary productivity. In addition, the optical data provide a good basis for exercising bio-optical models.

Finally, we intend to use the five-year moored array data set to deal with the central GBS question: what physical effects act to control recruitment? By about 2000, we expect that our biological colleagues can produce numbers on annual, Bank-averaged recruitment of cod and haddock, as well as populations of the key zooplankton species. These five-point (one number per year) time series can then be used with the moored array data to deal with central hypotheses. For example, is recruitment affected by stratification, ring intrusions or storminess, and at what critical times? Admittedly, a five-year time series may be too short to answer questions such as these, but we can at least expect to be able to eliminate some hypotheses. We anticipate, further, that our comprehensive data set will also open the door to other sorts of opportunistic interdisciplinary cooperations.

C. The Drifter Program (Limeburner and Beardsley, leaders)

The present Phase II grant provides funding for the field effort described above through September 1999. We request here funding to start October 1999 (year 2) to (a) complete the collection of ARGOS data for those drifters still functioning in our study area, (b)complete basic processing of all drifter position and temperature data and associated surface meteorological and satellite SST data used in our drifter trajectory animations, (c)construct and disseminate animations of the combined data via the GBS web site, and (d)analyze and synthesize the combined data and prepare manuscripts summarizing these results.

We plan to focus initial analysis efforts on:

We anticipate additional topics, especially related to the tidal mixing front, to arise as our analysis efforts intensify.

D. Underway ADCP Analysis (Flagg, leader)

Continued shipboard ADCP Data Collection and Processing:

Shipboard ADCP Analysis Projects:

E. Contemporary and Retrospective Hydrographic Data Analysis (Flagg,leader)

We plan analysis of historical and contemporary hydrographic data to define the decadal scale climatology of the Bank and the Northeast Channel, thus providing an historical context for the GBS. Of interest are decadal changes in slope water characteristics and whether the analyses of Gatien (1976) and Wright (1977), among others, concerning the relative location and character of the Labrador and western, or warm, slope waters, still pertain. We will determine whether there have been any changes in the Bank, slope, flank, or channel hydrography from the historical norm. Boothbay Harbor data (courtesy of Mark Lazzari) show about a one degree temperature increase during the early phase of the GLOBEC program and a transition to some of the highest temperatures seen this century. Petrie and Drinkwater (1993) attribute much of the long-term temperature (and salinity) variability on the Scotian shelf and within the Gulf to changes in the Labrador Current transport and/or changes in entrainment with surrounding waters. Thus hydrographic changes over the slope may also govern conditions on Georges Bank as well.