| The Effect of Varying Freshwater Inputs on Regional Ecosystems in the North Atlantic |
| Chai, Gangopadhyay and Haidvogel (Co-I: Bisagni, Curchister) | |
| PRS ROMS-PI Meeting | |
| SMAST -- Fairhaven | |
| March 19, 2009 |
| GLOBEC – Pan Regional Synthesis |
| ÒThe importance of comparative analysis in U.S. GLOBEC for pan-regional synthesis has been recognized from the inception of the program. Comparison of the dynamics of closely related taxa selected as target species in relation to specific physical processes (including stratification, mechanisms of retention and loss, upwelling and downwelling, and cross-front exchange) will be an integral component of the overall synthesis and integration effort in U.S. GLOBEC.Ó | |
| (U.S. GLOBEC Synthesis Implementation Plan, 2007). |
| Proposed Research |
| Comparing and contrasting the impact of freshwater influx to the eastern and western sides of the North Atlantic | |
| Understanding the development and maintenance of a possible three-gyre configuration of Calanus finmarchicus distribution in the North Atlantic | |
| Predicting the projected trends and variations in the North Atlantic Ocean based on IPCC projections for upcoming decades. |
| Interannual Variability |
| Question 1 |
| ÒAre the biophysical environments which sustain the populations of Calanus finmarchicus in the three gyres (WNA, NNA and NOR) of the North Atlantic connected to one another, and by what pathways and processes?Ó | |
| Question 1A |
| Are the nutrient and phytoplankton dynamics in these three gyres independent from one another (or not)? |
| Question 1B |
| What are the exchange rates among the three gyres, and do they control plankton dispersal across the North Atlantic Ocean? | |
| Question 2 |
| ÒHow significant is freshwater variability in determining the stratification and its subsequent impacts on primary productivity in the northern North Atlantic?Ó | |
| Question 2A |
| What are the relative roles of freshwater inputs compared with other local influences on stratification and mixing (e.g., E-P, heating/cooling, winds, etc.)? | |
| Question 2B |
| Are the ecosystem impacts of hydrologic variability related to large-scale changes in circulation patterns and the transports of the various North Atlantic current systems, which make up the different boundaries of the three-gyre system? | |
| Question 2C |
| What future changes are expected based upon IPCC projections of climate change? | |
| Approach |
| simulate basin-scale circulation fields for the GLOBEC decade of 1990-1999 using an eddy-resolving ROMS model extended to include sea ice and riverine inputs of fresh water | |
| validate these simulations with a new assemblage of hydrographic data and the synthesis study for the decade by Hakkinen and Rhines (2004) | |
| utilize a 10-component (lower trophic level) CoSINE biogeochemical model to understand the biophysical pathways connecting the three Calanus gyres during 1990-1999 |
| Approach (2) |
| forecast the next 20 years of the state of the North Atlantic Ocean using idealized forcing fields (wind curl, heat flux, E-P) representing IPCC scenarios of climate change | |
| Compile and use datasets on salinity, ice cover, IPCC scenarios, river discharge, hydrography, and Calanus abundances from the eastern and western North Atlantic to examine potential climate-related mechanisms influencing the Gulf Stream system, North Atlantic Current, and Calanus productivity and population dynamics in the North Atlantic Basin. | |
| GLOBEC P4B Results (Gangopadhyay, Bisagni, Batchelder and Gifford) |
| The basin-scale North Atlantic model is spun-up using Levitus climatology and forced with adjusted NCEP High and Low NAO fields – 2 validations | |
| The Gulf Stream position is northward (southward) during High (Low) NAO years | |
| LSW advection in the GOMGB region during 1997-98 after 1996 Low-NAO | |
| Slide 15 |
| Slide 16 |
| Slide 17 |
| NAO, GS Position and GS
Transport Parsons-Veronis Model |
| Parsons-Veronis model relates upstream GS transport as a function of GS separation [Gangopadhyay et al., 1992]. | |
| Higher transport results in earlier separation and vice versa | |
| Latitude of separation can be determined as a function of geostrophic transport (Tg) and transport due to Ekman drift (Te) which is derived from zonally integrated wind stress. | |
| Te estimated from NCEP-derived wind stress climatologies for high and low NAO phases. | |
| Parsons-Veronis model and NABM-derived transport induced GS separation latitudes are in agreement. | |
| GS transport response before separation is most likely forced by NAO-induced wind stress variation. Extensive research by other studies suggest GS transport response after separation is due to NAO-induced local wind stress curl variation. | |
| Slide 19 |
| Slide 20 |
| An Open Question |
| Publications |
| Chaudhuri, A.H., A. Gangopadhyay and J.J. Bisagni, 2008: Inter-annual Variability of Gulf Stream Warm Core Rings in response to the North Atlantic Oscillation, Accepted in CSR. | |
| Chaudhuri, A.H., A. Gangopadhyay, and J.J. Bisagni, 2009: Response of the western North Atlantic basin to characteristic high and low phases of the North Atlantic Oscillation, Submitted ms. | |
| 3 other short papers are in preparation. |
| Proposed Simulations |
| (i) run the high-resolution NAB model for 1990-1999 with sea ice and rivers | |
| (ii) compare this run with the existing Phase IVB run for both ENA and WNA | |
| (iii) run with active biogeochemistry | |
| (iv) validate the property fields while addressing biophysical subsets of Q1 and Q2 |
| Proposed Simulations (2) |
| Connectivity of the three-gyre system from a Lagrangian viewpoint – use ROMS floats | |
| Forecast studies based upon IPCC scenarios with a focus on surface forcing and freshwater input | |
| Simulations to be made available to the community | |
| Slide 25 |
| First Six Months |
| (i) reconfigure the NAB model for its enhanced domain size and inclusion of riverine inputs and sea ice; Run with SODA initial and Boundary conditions | |
| (ii) run low and/or high-resolution ROMS with linked CoSINE sub-model; | |
| and (iii) introduce freshwater forcing variability via the open boundary condition options within ROMS. |
| Slide 27 |
| Slide 28 |
| Arctic-Atlantic Model Resolution |
| Forcing and IBC Fields |
| Initial condition from SODA 1985 | |
| Boundary Condition – monthly SODA fields (1985-2008) | |
| CORE2 Forcing | |
| Ice and Rivers (Budgell, 2005) | |
| IPCC – 3 scenarios: A1F1(High), A1B(medium) and B1(low) |
| Slide 31 |
| SODA – 1985 fields -- Temp |
| Slide 33 |
| SODA -- Currents |
| Slide 35 |
| Future Work |
| Pan-Regional Synthesis on | |
| Understanding | |
| The Effect of Varying Freshwater Inputs on Regional Ecosystems in the North Atlantic |
|
| Seasonality – Boundary Condition |
| Salinity Boundary Condition - 1985 |
| Slide 39 |