Cruise Tracks and Ground Tracks: Enzyme Activity from Ship and Space

Abstract During the period of July 2004, ship-based measurements of alkaline phosphatase activity were made along the Louisiana shelf area of the Gulf of Mexico. This region is part of the Dead Zone, an area of continental shelf which experiences hypoxia (O 2 < 2 mL L -1 ) during periods of high flow and strong stratification. Five regions of interest were identified, based on whether the relative amount of activity was higher or lower than predictions made from nutrient and biomass concentrations. Satellite imagery (SST, true color, ocean color) from the period 8-20 July was used to identify regional circulation and biological patterns before and during the period of discrete sampling. Remotely sensed features support the idea of nutrient and biomass-dominated controls of activity. It was not capable of predicting variations in activity, however, perhaps due to extensive cloud cover and lack of quantitative satellite data during the discrete sampling period.

Primer on Ectoenzyme Activity Class of cell-surface enzymes used in the conversion of dissolved organic matter into inorganic nutrients Induced by nutrient depleted conditions Cleaves nutrient side group from the organic molecule, and the nutrient is subsequently taken up by the cell Can be used as indicator of nutrient stress Alk. Phos. Pi DOM Pi DOM

And the satellite bit? Ship-based measurements –simultaneous temperature, salinity, chlorophyll fluorescence, dissolved oxygen, current vectors, and nutrient concentrations –High sample resolution –Mostly weather-independent Satellite-based measurements –Synoptic coverage of a large region –Data preceding the sampling period In short, we would like satellite imagery to help provide a spatial and temporal framework for interpreting ship- based measurements.

Who’s involved? Oceansat-1… Polar, sun-synchronous orbit at an altitude of 720 km Orbital period is approximately 90 minutes, and has a revisit time of 48 hours Ocean Color Monitor (OCM) –8-channel imager for true color and ocean color at a resolution of 360 m –Pushbroom-based sampling scheme and has separate optics for each channel –Reflect certain properties of the water and atmosphere needed for ocean color measurements. absorption of colored dissolved matter (414 nm) off-peak absorption of chlorophyll a (443 nm) backscattering of suspended matter (670 nm) the absorption of atmospheric constituents (768, 867 nm)

Who’s involved? EOS Aqua… Near-earth (705 km), sun- synchronous polar orbit (98° inclination) orbital period of 99 minutes and a revisit period of 1-2 times per day Moderate Resolution Imaging Spectroradiometer (MODIS) –36 channels in the visible and infrared –resolution between m –Whiskbroom sampling scheme –5 calibration sources (4 on board, 1 deep space)

Who’s involved? GOES-12… Geostationary orbit (75° W), approximately km above the surface Imagery system consists of 1 visible and 4 IR channels ( um) Whiskbroom sampling scheme Resolution varies with wavelength and ranges from 1- 8 km Calibration is 1 internal source and a deep space signal SST acquired through radiance measurements –Converted into a blackbody temperature –Emmissivity corrections for SST

Points of Interest Location Number Inorganic Phosphate SalinityChlorophyllAP Activity 1HighLow 2 High 3 Low 4 HighLow 5HighLowHighLow

OCM Chlorophyll: Jul 16-20

OCM True Color: Jul 16-20

MODIS True Color: Jul 16-20

OCM True Color (2): Jul 16-20

GOES SST: Jul 16-20

NumberSSTOcean ColorTrue Color 15  3-4° coolingHighest levels near coast NA 2Cyclic coolingNA 34-5° local coolingIncrease?NA 4Western cold water?Decrease?NA 5Patchy cold water; no plume NA Location Number Inorganic Phosphate SalinityChlorophyllAP Activity 1HighLow 2 High 3 Low 4 HighLow 5HighLowHighLow

Discussion Ship-based measurements are currently not enough to predict activity based on nutrient concentration and/or biomass Satellite-based measurements support a nutrient/biomass explanation, but also do not allow prediction –Small, qualitative data set is an issue Rapid (≤ 2 day) variations in all remotely measured variables suggest limitations in spatial mapping

Futile…er, Future Work More/better images –Without clouds –Daily images Correlation between ocean color and discrete chlorophyll Quantify SST, ocean color data –Plot changes vs. time

References Christian, J. R., and D. M. Karl Bacterial ectoenzymes in marine waters: activity ratios and temperature responses in three oceanographic provinces. Limnology and Oceanography 40: Chrost, R. J Environmental control of the synthesis and activity of aquatic microbial ectoenzymes, p In R. J. Chrost [ed.], Microbial enzymes in aquatic environments. Springer. Martinez, J., and F. Azam Periplasmic aminopeptidase and alkaline phosphatase activities in a marine bacterium: implications for substrate processing in the sea. Marine Ecology Progress Series 92: Rabalais, N. N., R. E. Turner, Q. Dortch, D. Justic, V. J. Bierman, and W. J. Wiseman Nutrient-enhanced productivity in the northern Gulf of Mexico: past, present and future. Hydrobiologia 475: Sylvan, J. B., Q. Dortch, D. M. Nelson, A. M. Brown, W. Morrison, and J. W. Ammerman Phosphorus limits phytoplankton growth on the Louisiana shelf during hypoxia formation. Environmental Science & Technology 40: