Grace Su ( license@seawifs.gsfc.nasa.gov) (301) 286-9494
Applicant's Name: MATI KAHRU Institution: SCRIPPS INSTITUTION OF OCEANOGRAPHY Address: 9500 Gilman Dr. La Jolla, CA 92093-0218 Telephone: (858)534-8947 Fax Number: (858)822-0562 E-mail Address: mkahru@ucsd.edu Type of Temporary Agreement requested: An agreement that temporarily enables a non-real time SeaWiFS HRPT station to decrypt real-time data and release it to the Authorized Users list. Time period of temporary agreement: Dates (month/day/year): 01/07/2004 - 03/30/2004 SeaWiFS HRPT Station to provide data: HPAL List of Authorized Users to access real-time data. 1. MATI KAHRU 2. CHRISTOPHER DAVID HEWES 3. GREG B. MITCHELL Project Title: Plankton Community Structure and Iron Distribution in the Southern Drake Passage Principal Investigator(s): B.G. Mitchell Funding Agency(s): NSF, NOAA Description of the Research Project and Justification for Real-time SeaWiFS Data: The Shackleton Fracture Zone (SFZ) in Drake Passage defines a boundary between low and high phytoplankton waters. West of Drake Passage, southern Ocean waters south of the Polar Front and north of the Antarctic continent shelf have very low satellite-derived surface chlorophyll concentrations. Chlorophyll and mesoscale eddy kinetic energy are higher east of SFZ compared to values west of the ridge. In situ data from a 10-year survey of the reion as part of NOAA AMLR confirm the existence of a strong hydrographic and chlorophyll gradient in the region. We hypothesize that bathymetry, including the 2000 m deep SFZ, influences mesoscale circulation and transport of iron leading to the observed phytoplankton patterns. To address this hypothesis, we propose to examine phytoplankton and bacterial physiological states (including responses to iron enrichment) and structure of the plankton communities from virus to zooplankton, the concentration and distribution of Fe, Mn, and Al, and mesoscale flow patterns near the SFZ. Relationships between iron concentrations and phytoplankton characteristics will be examined in the context of the mesoscale transport of trace nutrients to determine how much of the observed variability in phytoplankton biomass can be attributed to iron supply, and to determine the most important sources of iron to pelagic waters east of the Drake Passage. Our goal is to better understand how plankton productivity and community structure in the Southern Ocean are affected by the coupling between bathymetry, mesoscale circulation, and limiting nutrient distributions. Rapid surface surveys of chemical, plankton, and hydrographic properties will be com;lemented by a mesoscale station grid for vertical profiles, water sampling, and bottle incubation enrichment experiments. Distributions of manganese and aluminum will be determined to help distinguish aeolian, continental shelf and upwelling sources of iron. The physiological state of the phytoplankton will be monitored by active fluorescence methods sensitive to the effects of iron limitation. Mass concentrations of pigment, carbon and nitrogen will be obtained by analysis of filtered samples, cell size distributions by flow cytometry, and species identification by microsopy. Primary production and photosynthesis parameters (absorption, quantum yields, variable fluorescence) will be measured on depth profiles, during surface surveys and on bulk samples from enrichment experiments. Viruses and bacteria will be examined for abundances, and bacterial production will be assessed in terms of whether it is limited by either iron or organic carbon sources. The proposed work will improve our understanding of processes controlling distributions of iron and the response of plankton communities in the Southern Ocean.