Susan Lozier Earth and Ocean Sciences Duke University National Science Foundation Observing the overturning in the subpolar North Atlantic: Implications for climate, biogeochemistry and the cryosphere

Meridional Overturning Circulation from an OGCM Wunsch (2002) Volume fluxes (Sv)

U.K. and U.S. RAPID/Mocha Monitoring Array Church (2007), Credit: Louise Bell and Neil White /CSIRO The program aims to continuously observe the strength of the Atlantic meridional overturning circulation (MOC) and ocean heat transport at 24°N in the North Atlantic. to measure the meridional overturning circulation (MOC) and ocean heat transport in the North Atlantic Ocean (Figure 1). These transports are primarily associated with the Thermohaline Circulation.

Temporal Variability of the Atlantic Meridional Overturning Circulation at 26.5°N Cunningham et al. (2007) Maximum northward transport of upper-layer waters on each day

Baehr et al. (2008) Correlation of the 26°N AMOC with other latitudes MOC from OGCM Wunsch (2002) Years: 1860 to 2000

U.S. AMOC Scientific Objectives The design and implementation of an AMOC monitoring system An assessment of AMOC’s role in the global climate An assessment of AMOC predictability

08/2007 US AMOC implementation plan: A transoceanic line in the subpolar North Atlantic that can capture the net transport of the overflow waters from the Greenland-Iceland- Norwegian Seas, as well as that from the Labrador Sea, should be a high priority. This observing system would be designed to complement the RAPID array at 26ºN, thereby providing measurements to evaluate intergyre connectivity within the North Atlantic. A similar array in the South Atlantic to provide an evaluation of interhemispheric connectivity is also a high priority. This monitoring system will not only lead to a better understanding of the mean state and variability of the AMOC, but may be used to detect whether an abrupt change in the AMOC is underway.

Participants at OSNAP workshop at Duke in April 2010 SheldonBaconNational Oceanography Centre, Southampton EmmanuelBossUniversity of Maine AmyBowerWoods Hole Oceanographic Institution TomDelworthGFDL, National Oceanic and Atmospheric Administration StefanGaryDuke University PatrickHeimbachMassachusetts Institute of Technology EricItsweireNational Science Foundation BillJohnsUniversity of Miami TorstenKanzowLeibniz Institute of Marine Sciences, University of Kiel CraigLeeUniversity of Washington DavidLeglerU.S. CLIVAR JohnLoderBedford Institute of Oceanography SusanLozierDuke University GalenMcKinleyUniversity of Wisconsin Mary JanePerryUniversity of Maine DetlefQaudfaselUniversity of Hamburg MonikaRheinUniversity of Bremen TobySherwinScottish Association for Marine Science FiammaStraneoWoods Hole Oceanographic Institution JimToddNational Oceanic and Atmospheric Administration JohnTooleWoods Hole Oceanographic Institution FranciscoWernerRutgers University IgorYashayaevBedford Institute of Oceanography

To quantify the large-scale, low-frequency, full water-column net fluxes of mass, heat and fresh water associated with the meridional overturning circulation in the subpolar North Atlantic. Overall goal of OSNAP: Overturning in the Subpolar North Atlantic Program

O-SNAP

Questions to address with OSNAP’s observing system include: a. What is the linkage between water mass production (Labrador Sea Water and the Norwegian-Greenland Sea Overflow Waters) and overturning in the subpolar North Atlantic? b. How does the downstream transport of overflow waters compare to the transport of these waters at their entry into the open Atlantic? c. What is the delivery of mass, heat and freshwater to the N-G Seas in the upper limb of the overturning circulation? d. What is the delivery of mass, heat and freshwater from the Arctic to the Labrador Sea? e. What is the relationship between overturning in the subpolar basin and overturning at 26°N? On what time scales are the overturning measures coherent? What is the overall spatial pattern of overturning in the Atlantic basin? f. What is the connectivity of the overflow waters within the boundary currents of the subpolar basin? Is the deep western boundary current a unique pathways for these waters?

Questions to address with complementary modeling efforts include: a. Are the observed overturning changes in the subpolar and subtropical North Atlantic consistent with the known forcing fields? Can a dominant mechanism for the seasonal and interannual variability be identified? b. What is the connectivity of the overturning variability across the Atlantic basin?

The primary interdisciplinary linkages for this planned program are with biogeochemistry, ocean biology and the cryosphere. The focus of this linkage is predicated on three main questions: a. What are the mechanisms controlling CO 2 uptake in the subpolar North Atlantic and how do they vary on seasonal and interannual time scales? How does ocean physics, particularly the AMOC, constrain this uptake? b.What are the spatial and temporal patterns of primary productivity in the North Atlantic on seasonal and interannual time scales? How does ocean physics, including AMOC variability, constrain the productivity? c. What is the linkage between poleward heat transport in the subpolar basin and Arctic sea- ice reduction? Between poleward heat transport in the subpolar basin and mass loss from the Greenland Ice Sheet?

What are the mechanisms controlling CO 2 uptake in the subpolar North Atlantic and how do they vary on seasonal and interannual time scales? How does ocean physics, particularly the AMOC, constrain this uptake? Annual air-sea carbon dioxide flux (positive out) using gridded data from Takahashi et al. (2009). The North Atlantic is a strong sink for atmospheric carbon dioxide (Takahashi et al., 2009) and it dominates storage of anthropogenic carbon in the ocean (Sabine et al., 2004). On an annual basis the Atlantic as a whole accounts for 41% of the global air-sea CO 2 flux and nearly half of this flux occurs north of 50 ° N (Figure 1). This high flux is driven by a combination of the AMOC and a strong, annual cycle of net community production (NCP) (Schuster and Watson, 2007; Kortzinger et al., 2008). The AMOC drives northward flow of warm surface waters. As these waters cool, they absorb additional CO 2 and then leave the surface as deep waters form.

What are the spatial and temporal patterns of primary productivity in the North Atlantic on seasonal and interannual time scales? How does ocean physics, including AMOC variability, constrain the productivity? Doney, S.C., Plankton in a warmer world. Nature, (2006).

What is the linkage between poleward heat transport in the subpolar basin and Arctic sea-ice reduction? Between poleward heat transport in the subpolar basin and mass loss from the Greenland Ice Sheet? How does freshwater export from Hudson Strait and Davis Strait collectively impact the stratification of waters in the Labrador Sea? F. Straneo and S. Lentz (WHOI) From Straneo and Saucier, 2008

OSNAP Intersection with BASIN: Basin- scale Analysis, Synthesis, and INtegration

Theme 1. How will climate variability and change influence the seasonal cycle of primary productivity, trophic interactions, and fluxes of carbon to the benthos and the deep ocean? What aspects of the physical system are changing with climate variability and change (for example changes in temperature, stratification, transport, acidification)? How will the biogeochemical processes and ecosystem’s responses to these changes differ across the basin and among the shelf seas? How are the populations of phytoplankton, zooplankton, benthos, and higher trophic levels influenced by large-scale ocean circulation and what is the influence of changes in atmospheric and oceanic climate on their population dynamics and diversity? What are the feedbacks from changes in ecosystem structure and dynamics on climate signals? Theme 2. How do behavior and life history strategies of target organisms, including vertical and horizontal migration, contribute to observed population dynamics, community structure, and biogeography? Theme 3. How does the removal of exploited species influence marine ecosystems and sequestration of carbon? BASIN Themes from Implementation Plan 1/11

Red lines: Boundary monitoring partially implemented. The two red lines are (i) the German Labrador Sea Exit array, which would need to be extended both to near-surface and inshore on the shelf, and (ii) the Ellett Line, which needs improved temporal and spatial measurement density. Green line: Site of past boundary monitoring: not presently in the water. The green line is the location of the UK DWBC and French EGC arrays, in the water between 2004 and Some engineering development is required to enable robust shelf monitoring here. Proposed seaward termination of this line is the planned OOI Irminger Sea Global-Scale Node (GSN) at 60°N, 39°W. Blue line: Approximate location of a possible Mid-Atlantic Ridge array. Yellow lines: Ocean regions to be monitored by “soft” arrays, comprising of a mixture of gliders, floats, possibly deep T/S moorings, BPRs and bottom current meters. The observing design for the interior is currently being studied to assess the mix of instrumentation that can most efficiently accomplish the needed spatial and temporal coverage. O-SNAP OSNAP design elements

O-SNAP US/UK Cape Farewell Array US/Canada Cape Desolation Array German 53⁰N Array UK Ellett Line Array OSNAP West OSNAP East ---- “Soft” lines: US Netherlands: Reykjanes Ridge Array OOI

OSNAP Partners U.S. Physics: Amy Bower (WHOI), Patrick Heimbach (MIT), Bill Johns (U. Miami), Craig Lee (UW), Susan Lozier (Duke), Bob Pickart (WHOI), Steve Riser (UW) and Fiamma Straneo (WHOI) U.S. Biogeochemistry and Biology: Ken Johnson (MBARI), Galen McKinley (UW), Mary Jane Perry (U. Maine) and Emmanuel Boss (U. Maine) International Partners (leads): UK: Sheldon Bacon and Stuart Cunningham Canada: John Loder Germany: Torsten Kanzow Netherlands: Laura de Steur

OSNAP Timeline 1. UK-OSNAP planning meeting, early March 2011 NOC, Southampton Sheldon Bacon, organizer 2. OSNAP West planning meeting, 4/26-27, 2011 Bedford Institute of Oceanography John Loder, organizer 3. OSNAP East planning meeting, 4/6, EGU Meeting, Vienna Susan Lozier and Fiamma Straneo, organizers

OSNAP Timeline, cont. Submission of OSNAP physics: August 2011 Submission of OSNAP biogeochemistry: February 2012 In the water: Summer 2013

Summary OSNAP addresses a high priority of the U.S. AMOC program, which was developed to meet 1 of 4 near-term priorities of the 2007 ORPP. OSNAP will enable answers to fundamental questions regarding ocean overturning. OSNAP leverages existing measurement systems; interface w/ OOI. OSNAP has garnered significant international interest and collaboration. OSNAP is a multi-disciplinary observing program that will investigate physical constraints on biogeochemistry, marine ecosystems and the cryosphere. Available: U.S. AMOC Implementation Plan, U.S. AMOC annual reports, OSNAP progress report; OSNAP biogeochemistry white paper (in prep)