Jaime Palter Susan Lozier Dick Barber

1. The role of Eighteen Degree Water in establishing the North Atlantic nutrient reservoir:Adding nutrient analyses to the CLIMODE hydrography and moorings Jaime Palter Susan Lozier Dick Barber

2. [NO-3] T 32°N 64°W 7/1989 BATS 32°N 64°W 7/1960 Hydro S 3 30°N 52°W 7/1997 16°N 52°W 7/1997 Downstream impact of EDW on the nutrient reservoir is visible in example profiles from BATS and WOCE sections

3. A wedge of uniform density, low-nitrate EDW resides below the euphotic zone. At the edge of the EDW PV minima, there is a clear front in nitrate.

4. The PV-nitrate relationship, at the PV minima, along the WOCE sections and for the time series data

5. Annual mean chlorophyll Biological impact The annual mean chlorophyll minimum coincides with the EDW location, shown to depress and weaken the nutricline. PV on  = 26.5

6. Summary of EDW impact on nutrient reservoir • The formation and advection of EDW pycnostad cause the depression of the NA subtropical pycnocline and nutricline • The pycnostad itself is relatively low in nutrients, so above the depressed nutricline the inserted EDW is a low concentration "nutristad." • The presence of the depleted EDW damps biological response to the vertical processes that flux sub-euphotic zone water upward. • As EDW transits the gyre, its low nutrient signature is destroyed by mixing processes and as a result of the sinking and remineralization of organic matter

7. Objectives of CLIMODE collaboration • Directly evaluate the hypothesis that EDW is depleted in nutrients during formation and exported with a low nutrient signature • Quantify the flux of nutrients to the surface by entrainment of thermocline water into the ML during convection • 3) Illuminate the time scale of biological depletion of inorganic nutrients during EDW formation • 4) Observe the downstream decay of the nutrient signature as it transits the gyre.

8. Field Measurements and Data Analysis • Ship-based nutrient sampling (nitrate, nitrite, silicate, phosphate, and ammonium) • ODF accompanying 1st cruise—Jan/Feb 2006 • Freezing samples on Feb/Mar cruises 2007 • Collect and freeze samples for Sigman Lab to conduct nitrogen fixation study • Nutrient time series at the moored profiler stations • Deploying Satlantic’s ISUS nitrate sensor at 50m—Nov 2005 • Recovering, servicing and redeploying—Nov 2006 • Analyze BATS nutrient data, in conjunction with float data, to look at the destruction of EDW during gyre transit

9. Mooring configuration ISUS sensor 50m Profiler stop

10. Relative time scales in the nitrate conservation equation + = - Local time rate of change Sources & sinks Horizontal diffusion Vertical diffusion Advection = + + + Peclet number, the ratio of the vertical diffusive time scale to the horizontal advective time scale, UD2/Lkv 103. The ratio of the remineralization time scale to the advective time scale, UN /LR  1 – 5, reflecting an important competition between these processes.

11. Nitrate and CFC age are both significantly correlated to PV.