Discussion 2

Leader: R. Beardsley
Rapporteur: J. Bisagni

“Hot Topics” & Phase IV Announcement of Opportunity

A discussion of “hot topics” was initiated on day 3 of the Scientific Investigators' Meeting with the idea that some or all of the topics might be incorporated into the Phase IV Announcement of Opportunity (AO) to be released sometime during summer 2000 after approval by the US-GLOBEC Scientific Steering and Executive Committees during spring 2000. Also discussed was a tentative Phase IV proposal due date of mid-December 2000 which would then enable an overlap of 6 to 12 months for new Phase IV projects with existing Phase III projects.

The primary objective of this session was to produce a list of “hot topics” that might benefit from a “synthesis” of data and models through collaborations between both existing and new scientific investigators, i.e., “What areas of research will benefit most from collaboration?” In order to answer this question, a group meeting was initiated for all meeting attendees through presentation of a series of discussion points as outlined below.

1) Possible Climate Connections With the North Atlantic Oscillation (NAO)

Biological effects:

Changes in Georges Bank zooplankton displacement volume (as identified from MARMAP and discussed by D. Mountain) are correlated directly with NAO index.

Changes in the abundance of C. finmarchicus in the Gulf of Maine appeared to be inversely correlated with NAO index as discussed by C. Greene.

What can C. finmarchicus abundance measurements made by the continuous plankton recorder (CPR) tell us about a climate link?

What about the effect of NAO on other aspects of the biological oceanography in the region?

Is there a consistent mechanism/explanation for all of these signals?

Physical effects:

Lowering of salinity through 1996 on Georges Bank and in the Gulf of Maine and some inter-annual variability as discussed by D. Mountain from Georges Bank broad-scale survey data may be related to climate factors.

Changes in the source of fresh water to Georges Bank as evidenced by oxygen isotope and other data as presented by R. Houghton may also be related to climate factors.

The shift in the Labrador Slope Water boundary during 1997-1998 as discussed by P. Smith may be related to NAO index.

What are the important pathways, time scales, and mechanism(s)?

Do any of the large-scale general circulation models depict changes in the Labrador Slope Water?

2) Spatial/temporal distributions of C. finmarchicus

What are the life history events and physics that determine the flow of C. finmarchicus through the western Scotian Shelf/Gulf of Maine/Georges Bank system?

More specifically, where, when, and how do C. finmarchicus diapause and then return to the Georges Bank/Gulf of Maine system?

What is the role of strong, but infrequent physical (wind) forcing on these sources and sinks?

3) Vital rates and diet

Rates of ingestion, egg production, and (maybe) growth and indices of condition (RNA/DNA) indicate that C. finmarchicus is living sub-optimally in an environment that appears to be replete with appropriate food most of the time.

Why does C. finmarchicus appear to do so poorly on Georges Bank for so much of the time?

What are the spatial and temporal distributions of vital rates (ingestion, egg production, growth, mortality) of target taxa (C. finmarchicus, larval fish)?

Can measured vital rates be integrated with existing physical and population dynamics models?

To what extent is chlorophyll standing stock a proxy for potential food environment on Georges Bank?

4) Recent haddock (M. aeglefinus) recruitment success

Haddock recruitment during 1998 (and possibly 1999) was excellent as discussed by S. Murawski from NOAA/NMFS survey data.

Why was haddock recruitment so successful during spring 1998?

Why didn’t similar recruitment success occur for cod (G. morhua) as well?

Did the environment differ during April-May 1998 to enhance survival?

5) Shelf/slope frontal intrusions sampled during US-GLOBEC Phases I-III

Major events occurred during 1995, 1997, and 1999 when anomalous waters intruded onto southern Georges Bank from the slope water region, displacing shelf water as observed by many workers.

What is the frequency and inter-annual variability in the occurrence of these frontal intrusions?

What is the causative mechanism(s)?

What are the immediate and lasting effects (if any) on the Georges Bank hydrography and biology?

What is the cross-shelf extent on Georges Bank of biological losses due to instabilities of the shelf/slope front or warm core Gulf Stream ring streamers?

6) Scotian Shelf Water to Georges Bank across Northeast Channel

What is the frequency and inter-annual variability in the occurrence of these cross-overs?

What is the causative mechanism(s)?

What are the immediate and lasting effects (if any) on the Georges Bank hydrography and biology?

7) Georges Bank tidal mixing front

What is the seasonal evolution of the position and structure of the front?

What is the kinematics of the secondary circulations near the front and how do they differ in the along- and cross-isobath directions?

What are the effects of the low-frequency flows on the southern flank of Georges Bank?

Can a tidal model be developed that can de-tide both the physics and biology adequately?

Can frontal models reproduce the observed currents accurately including results from dye tracer studies?

8) Georges Bank buoyancy, tidal and wind-driven responses

What are their effects on physical, chemical and biological properties?

9) Internal solitary waves (solitons)

Can we describe and model the generation, propagation and dissipation of solitons?

What is the potential of solitons for vertical mixing and nutrient fluxes, altering predator-prey encounter rates, on-Bank transport and retention of organisms, and mixing near the tidal mixing front?

What are the effects of bottom-trapped solitons within the bottom boundary layer?

10) A new larval fish paradigm

11) Relationship of events to decadal variability

What links exist (if any) between events on Georges Bank during the GLOBEC field years 1995-99 and longer-time, larger-spatial scale variability?

12) Flow-thru versus Local System

In a physical sense, Georges Bank can be thought of as a flow-thru system. Water properties on the Bank are driven by upstream flow on the Scotian Shelf and slope.

To what extent does the concept of a flow-thru system apply to the target species?