Bipolar Atlantic Thermohaline Circulation (BIAC) a IPY proposal coordinated by Tor Gammelsrød Geophysical Institute, University of Bergen

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1 Bipolar Atlantic Thermohaline Circulation (BIAC) a IPY proposal coordinated by Tor Gammelsrød Geophysical Institute, University of Bergen The role of the Thermohaline Circulation (THC) as a driving force for the ocean circulation, and therefore the global climate, is well acknowledged. The majority of the deep- and bottom- water production takes place in the Atlantic sector. The densest water ventilating the world ocean abyss is produced in the northern and southern extremes. When the dense water is cascading towards great depths, it mixes with surrounding water masses to produce the various brands of bottom water. The replacement of the surrounding water is believed to be an important driving force for the global THC. The BIAC concentrate on all aspects related to bottom water formation and THC in the past, present and future. Modelling and remote sensing are important tools, as well as in situ measurements that will require adequately equipped icebreakers and moorings.

2 Salinity Temperature

3 Bipolar Atlantic Thermohaline Circulation (BIAC) The aim of the proposed project is to study mechanisms, manifestations and impacts of bottom water formation on the bipolar Atlantic Ocean shelves. Key areas are the Barents Sea, and the southern Weddell Sea. Objectives Identify locations where dense water is formed (open ocean, shallow shelves) Study dense water formation processes; cooling, ice formation, convection Identify dense water pathways on shelves and in semi-closed basins Study the cascading of dense water towards the deep ocean. Define physical and biogeochemical controls on ocean carbon biogeochemistry Investigate relationships between variability in deep-water formation, CO2 uptake rates and large-scale natural or anthropogenic climate forcing Obtain paleo-records of dense-water formation rates

4 The Bipolar Atlantic Ocean Ventilation areas Key areas

5 Budget: 44.7 mil NOK

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7 The Arctic Ocean ventilation area The Barents Sea Cruises Cruises

8 The Cradle of the Bi-polar Atlantic Ocean THC Bottom water The southern Weddell Sea... ISW + WDW = 4 Sv WSBW (-0.8 C) WSBW AABW 1.6 ± 0.5 Sv ISW (Foldvik et al 2004) DEEP WATER FORMATION IN THE WEDDELL SEA Filchner Depression CMR-IFIX Østerhus 9811

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10 Low latitude Downslope processes and Thermohaline Circulation Compensating flow Mixing Sv Vent.: 4-6 Sv Labrador Sea NADW 3 C Surface outflow 3 Sv Entrainment 12 Sv 6 Sv 6 C Atlantic inflow O v erfl ow Greenland Scotland Ridge Cooling 6 Sv Overflow Water 0 C Ventilation Upwelling Freshwater Arctic

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12 IPY station on the Filchner-Ronne Ice shelf? The role played in the climate system by the interaction between the ocean and Antarctic ice shelves is a key issue regarding future climate changes. To establish a long term (several decades) monitoring station on the Filchner- Ronne Ice Shelf, in the southern Weddell Sea will be consider proposed under BIAC. Technology! IFIX Inductive Oceanographic Sensor Chain Atlantic Ocean Weddell Sea Ic e Sheet Antarc tica Pacific Ocean Ross Sea Controller and Dual Satellite Link Current Meter Salinity, Temperature and P ressure (CTP) Sensor

13 BIAC links to other IPY projects BIAC

14 BIAC IPY Cluster # 23

15 The Bipolar Atlantic Ocean THC/MOC Low latitude Surface outflow 3 Sv Cooling Freshwater Arctic Salinity Compensating flow Upwelling Mixing Sv Vent.: 4-6 Sv Labrador Sea NADW 3 C Entrainment 12 Sv 6 Sv 6 C Atlantic inflow O v erfl ow Greenland Scotland Ridge 6 Sv Overflow Water 0 C Ventilation 1000 Temperature

16 BIAC WT1. Regional circulation and forcing - preconditioning and variability WT2. Sea ice freezing and high-salinity shelf water (HSSW) formation WT3. Downslope processes pathways, cascading and mixing WT4. Contribution to the thermohaline circulation (THC) and consequences for the climate WT5. Future long term changes at key monitoring locations Budget 44.7 mill NOK