Impacts of Climate and basin-scale variability on the seeding and production of Calanus finmarchicus in the Gulf of Maine and Georges Bank

Avijit Gangopadhyay

With Bisagni, Gifford and Batcheldar

GLOBEC meeting, WHOI

23 April 2007

List of Investigators

Avijit Gangopadhyay (PI – Basin-scale physical modeling)

Jim Bisagni (UMass Dartmouth) – Satellite SST field, Hydrographic analysis

Dian Gifford (URI) – Zooplankton data analysis

Hal Batchelder (OSU) – IBM modeling

Goals and Objectives

to probe the connections between Calanus finmarchicus distributions and the physical oceanographic properties, climate variability, and basin-scale circulation changes that are likely to affect the copepod’s transport onto Georges Bank.

We will do this using a combination of numerical model simulations and observational data.

Bio-physical Hypotheses

Hypothesis: The occurrence of large populations of Calanus finmarchicus in the coupled GB/GoM system REQUIRES (1) high seed stocks (supply) of diapausing C.finmarchicus in the deeper ocean regions nearby (GOM basins and the Slope Sea), (2) that the deep C. finmarchicus stocks terminate diapause at the appropriate time to be synchronous with continental shelf spring blooms, and (3) a nutrient enriched, highly productive ecosystem in the GB/GoM to sustain high growth and survival rates of Calanus that will provide seed for the subsequent year.

Prediction A: Overwintering Calanus finmarchicus seed stocks are LOW and GB/GoM productivity is HIGH when the water masses of the Slope Sea have little influence (input) from Labrador-Irminger Gyre (Labrador Slope Water) water masses (due to the relatively nutrient replete bottom waters and low Calanus supply in Warm Slope Waters), but C. finmarchicus recruitment is good because of a near-perfect match between the time of diapause awakening and the time of the spring bloom, the latter of which is large because of the higher concentration of nutrients in deep warm slope waters.

Prediction B: Overwintering C. finmarchicus seed stocks are HIGH and GB/GoM productivity is LOW when the water masses of the Slope Sea have a large proportion of Labrador Sea water (due to the relatively nutrient-depleted bottom waters and high C. finmarchicus supply in cold Labrador Slope Water), but recruitment and productivity are poor because of the generally low springtime productivity (low nutrients) and a timing mismatch between diapause awakening, ascent and reproduction and the NW Atlantic spring bloom.

Methodology

Set up and run an individual based model (IBM) for the Northwest Atlantic, using the high-NAO (1980-1993) and low-NAO (1962-1971) forced physical fields from an ongoing eddy-resolving North Atlantic simulation.

Perform a set of eddy-resolving basin-scale model simulations during 1988-1999 starting from already existing high-NAO simulations (from the ongoing NASA project) and run the IBM to study the interannual variability of C. finmarchicus seeding and production in this region.

Analyze long-term in-situ physical and biological datasets and satellite-derived sea surface temperature (SST) along with in-situ physical, biological, and chemical data collected during the GLOBEC core-measurement period (1995-1999), and validate the basin-scale physical and biological fields to develop a broader understanding of C. finmarchicus seeding and production.

Generate four-dimensional high-resolution (5-km) physical fields using basin-scale fields and available data during 1993-1999, and run a series of IBM simulations at higher resolution in order to address questions relating ecosystem variability on the Scotian Shelf, on Slope Sea and within the Gulf of Maine and on Georges Bank to the large-scale fluctuations of the NAO.

Ongoing NASA project

Basin scale modeling for North Atlantic

High and Low NAO simulations

Focus on Gulf Stream and Labrador Sea

Nutrient Dynamics – Depletion vs. Dilution

Physics and nutrient flux experiments

ROMS North Atlantic Model

North Atlantic Heat Flux

North Atlantic Heat Flux

Net Heat Flux is given as

Q_net = Q_H+Q_E+Q_LW+Q_SW

where,

Q_H = Sensible Heat Loss

Q_E = Latent Heat Loss

Q_LW = Longwave Loss

Q_SW = Shortwave Heat Gain

Is the NCEP climatology underestimating/overestimating any of these components?

North Atlantic Heat Flux

The NCEP Climatology overestimates the Net Heat Loss for the North Atlantic Region due to overestimation of Latent and Sensible Heat Loss terms and underestimation of Shortwave Gain term.

This overestimation is leading to spurious results in the Low NAO Model simulation.

Functional regression is used resolve the overestimation in NCEP Climatology as follows:

Slope (m) and Intercept (y) are determined for each month using the SOC and NCEP climatologies for 1980-1993 (High NAO)

SOC(high NAO) = m*NCEP(high NAO) + y

m and y are used to adjust the NCEP Climatology for 1958-1971 (Low NAO)

Predicted NCEP (low NAO) = m*NCEP(low NAO) y, also

Predicted NCEP (high NAO) = [SOC(high NAO)-y] / m

North Atlantic Heat Flux

Model Results

Hypothesis

The Gulf Stream position is northward (southward) during High (Low) NAO years.

The model is spun-up using Levitus climatology for the North Atlantic Basin and subsequently forced with adjusted NCEP High and Low NAO fields.

GS mean positions are computed at different depths for both High and Low NAO simulations for comparison

Gulf Stream path analysis

Isotherms typical of Gulf Stream signature at different depths are used to obtain frontal location.

Nearest neighbor connected component theory is used to ascertain to continuity of the front

Frontal location derived from every 3 day model output are averaged to obtain mean frontal position

Slide 17

Upper Layer Integrated Path

Model simulation validates our hypothesis that GS is northward (southward) during High (Low) NAO years

Current/Future Work

The High NAO simulation will be used as initial condition to run the ROMS model for GLOBEC years (1995-1999)

SOC forcing available from 1980-1999 will be used to force the model instead of the NCEP climatology

Model output will be used to track the 1998 event of southwestward inflow of Labrador Current

Melding of ROMS with FORMS for 1995-1999 using 5-day SST fields

Proposed Biological simulations

Individual-based models (HPB)

Lagrangian pathways

Zooplankton data as initial and validation fields (DG)

Seeding vs. production hypothesis testing

Impact of Labrador water inflow on Slope sea and GOMGB regions

Creating high resolution fields

Use Feature oriented regional modeling system (FORMS) for GOMGB (Gangopadhyay et al., 2003; Brown et al. 2007a-b)

270 non-dimensional structure functions for temperature and salinity along and across seven features in the Gulf/Bank

Calibrate with SST 5-day composite (Bisagni’s lab)

Use basin-scale simulations as background

Multiscale Objective analysis will meld basin-to-regional scale fields

Use these high-resolution fields for biological simulations

Summary

NASA-funded Basin-scale simulation is complete

Wind forcing fields during 1980-1999 are ready and are being used to force the model for different simulations

Will use this set-up to start GLOBEC period simulations and nowcasting

Biological IBM towards understanding impact of climate and BSV on calfin seeding and production


	Avijit Gangopadhyay
	With Bisagni, Gifford and Batcheldar
	GLOBEC meeting, WHOI
	23 April 2007


	Avijit Gangopadhyay (PI – Basin-scale physical modeling)
	Jim Bisagni (UMass Dartmouth) – Satellite SST field, Hydrographic analysis
	Dian Gifford (URI) – Zooplankton data analysis
	Hal Batchelder (OSU) – IBM modeling


	to probe the connections between Calanus finmarchicus distributions and the physical oceanographic properties, climate variability, and basin-scale circulation changes that are likely to affect the copepod’s transport onto Georges Bank.
	We will do this using a combination of numerical model simulations and observational data.


	Hypothesis: The occurrence of large populations of Calanus finmarchicus in the coupled GB/GoM system REQUIRES (1) high seed stocks (supply) of diapausing C.finmarchicus in the deeper ocean regions nearby (GOM basins and the Slope Sea), (2) that the deep C. finmarchicus stocks terminate diapause at the appropriate time to be synchronous with continental shelf spring blooms, and (3) a nutrient enriched, highly productive ecosystem in the GB/GoM to sustain high growth and survival rates of Calanus that will provide seed for the subsequent year.


	Prediction A: Overwintering Calanus finmarchicus seed stocks are LOW and GB/GoM productivity is HIGH when the water masses of the Slope Sea have little influence (input) from Labrador-Irminger Gyre (Labrador Slope Water) water masses (due to the relatively nutrient replete bottom waters and low Calanus supply in Warm Slope Waters), but C. finmarchicus recruitment is good because of a near-perfect match between the time of diapause awakening and the time of the spring bloom, the latter of which is large because of the higher concentration of nutrients in deep warm slope waters.
	Prediction B: Overwintering C. finmarchicus seed stocks are HIGH and GB/GoM productivity is LOW when the water masses of the Slope Sea have a large proportion of Labrador Sea water (due to the relatively nutrient-depleted bottom waters and high C. finmarchicus supply in cold Labrador Slope Water), but recruitment and productivity are poor because of the generally low springtime productivity (low nutrients) and a timing mismatch between diapause awakening, ascent and reproduction and the NW Atlantic spring bloom.


	Set up and run an individual based model (IBM) for the Northwest Atlantic, using the high-NAO (1980-1993) and low-NAO (1962-1971) forced physical fields from an ongoing eddy-resolving North Atlantic simulation.
	Perform a set of eddy-resolving basin-scale model simulations during 1988-1999 starting from already existing high-NAO simulations (from the ongoing NASA project) and run the IBM to study the interannual variability of C. finmarchicus seeding and production in this region.
	Analyze long-term in-situ physical and biological datasets and satellite-derived sea surface temperature (SST) along with in-situ physical, biological, and chemical data collected during the GLOBEC core-measurement period (1995-1999), and validate the basin-scale physical and biological fields to develop a broader understanding of C. finmarchicus seeding and production.
	Generate four-dimensional high-resolution (5-km) physical fields using basin-scale fields and available data during 1993-1999, and run a series of IBM simulations at higher resolution in order to address questions relating ecosystem variability on the Scotian Shelf, on Slope Sea and within the Gulf of Maine and on Georges Bank to the large-scale fluctuations of the NAO.


	Basin scale modeling for North Atlantic
	High and Low NAO simulations
	Focus on Gulf Stream and Labrador Sea
	Nutrient Dynamics – Depletion vs. Dilution
	Physics and nutrient flux experiments


	Net Heat Flux is given as
	Q_net = Q_H+Q_E+Q_LW+Q_SW
	where,
	Q_H = Sensible Heat Loss
	Q_E = Latent Heat Loss
	Q_LW = Longwave Loss
	Q_SW = Shortwave Heat Gain
	Is the NCEP climatology underestimating/overestimating any of these components?


	The NCEP Climatology overestimates the Net Heat Loss for the North Atlantic Region due to overestimation of Latent and Sensible Heat Loss terms and underestimation of Shortwave Gain term.
	This overestimation is leading to spurious results in the Low NAO Model simulation.
	Functional regression is used resolve the overestimation in NCEP Climatology as follows:
	Slope (m) and Intercept (y) are determined for each month using the SOC and NCEP climatologies for 1980-1993 (High NAO)
			SOC(high NAO) = m*NCEP(high NAO) + y
			m and y are used to adjust the NCEP Climatology for 1958-1971 (Low NAO)
			Predicted NCEP (low NAO) = m*NCEP(low NAO) y, also
			Predicted NCEP (high NAO) = [SOC(high NAO)-y] / m


	The Gulf Stream position is northward (southward) during High (Low) NAO years.
	The model is spun-up using Levitus climatology for the North Atlantic Basin and subsequently forced with adjusted NCEP High and Low NAO fields.
	GS mean positions are computed at different depths for both High and Low NAO simulations for comparison


	Isotherms typical of Gulf Stream signature at different depths are used to obtain frontal location.
	Nearest neighbor connected component theory is used to ascertain to continuity of the front
	Frontal location derived from every 3 day model output are averaged to obtain mean frontal position


	Model simulation validates our hypothesis that GS is northward (southward) during High (Low) NAO years


	The High NAO simulation will be used as initial condition to run the ROMS model for GLOBEC years (1995-1999)

	SOC forcing available from 1980-1999 will be used to force the model instead of the NCEP climatology

	Model output will be used to track the 1998 event of southwestward inflow of Labrador Current

	Melding of ROMS with FORMS for 1995-1999 using 5-day SST fields


	Individual-based models (HPB)
	Lagrangian pathways
	Zooplankton data as initial and validation fields (DG)
	Seeding vs. production hypothesis testing
	Impact of Labrador water inflow on Slope sea and GOMGB regions


	Use Feature oriented regional modeling system (FORMS) for GOMGB (Gangopadhyay et al., 2003; Brown et al. 2007a-b)
	270 non-dimensional structure functions for temperature and salinity along and across seven features in the Gulf/Bank
	Calibrate with SST 5-day composite (Bisagni’s lab)
	Use basin-scale simulations as background
	Multiscale Objective analysis will meld basin-to-regional scale fields
	Use these high-resolution fields for biological simulations


	NASA-funded Basin-scale simulation is complete
	Wind forcing fields during 1980-1999 are ready and are being used to force the model for different simulations
	Will use this set-up to start GLOBEC period simulations and nowcasting
	Biological IBM towards understanding impact of climate and BSV on calfin seeding and production