| Lohrenz, S, E, University
of Southern Mississippi, Stennis Space Center, MS 39529, USA, Steven.Lohrenz@usm.edu |
| Redalje, D, G, University of Southern
Mississippi, Stennis Space Center, MS 39529, USA, Donald.Redalje@usm.edu |
| Verity, P, G, Skidaway Institute of
Oceanography, Savannah, GA 31411, USA, peter@skio.peachnet.edu |
| Flagg, C, , Brookhaven National Laboratory, Upton,
NY 11973, USA, flagg@bnl.gov |
|
| SEASONAL CONTRASTS IN BIOMASS AND PRIMARY PRODUCTION OVER
THE CONTINENTAL SHELF OFF CAPE HATTERAS, NORTH CAROLINA |
 |
| Coastal margins are frequently regions of high primary
production and subject to variability from both natural and anthropogenic
forcing. As part of DOE- and NSF-sponsored research, we conducted studies
during March and July of 1996 of spatial and temporal patterns of
chlorophyll and primary production in continental shelf waters off Cape
Hatteras, North Carolina. Primary production was determined using a
wavelength-resolved photosynthesis-irradiance model. Highest chlorophyll
concentrations during March were located in a mid-shelf region
corresponding to an area of intermediate salinities. Cross-shelf sections
revealed high subsurface concentrations near the shelf break. In July,
chlorophyll concentrations were generally lower. Highest water column
integrated primary production during March (>2.5 gC/m2/d) was observed
near the shelf break. In contrast, highest values in July (>3 gC/m/d)
were associated with low salinity inner shelf water. The high spring
productivity at the shelf break was dominated by larger (>8 micron)
phytoplankton and nutrient data suggest this feature may be a consequence
of upwelling at the shelf break. This productivity may be quantitatively
important in the overall carbon/nitrogen budget of the southern
Mid-Atlantic Bight shelf. |
|
| Back to Biogenic Elements |
|
| Redalje, D, G, The
University of Southern Mississippi, Stennis Space Center, USA, Donald.Redalje@usm.edu |
| Lohrenz, S, E, The University
of Southern Mississippi, Stennis Space Center, USA, Steven.Lohrenz@usm.edu |
| Verity, P, G, Skidaway
Institute of Oceanography, Savannah, USA, peter@skio.peachnet.edu |
| Holtermann, K, , The University
of Southern Mississippi, Stennis Space Center, USA, holterma@ssc.usm.edu |
|
| PHYTOPLANKTON COMMUNITY STRUCTURE WITHIN A
DISCRETE WATER MASS IN THE COASTAL WATERS OFF CAPE HATTERAS, NORTH
CAROLINA |
|
| As part of the Ocean Margins Program, we
examined the biogeochemical cycling of carbon within discrete coastal
water masses off Cape Hatteras, North Carolina. Drogues set at 10 meters
were followed and water sampled daily from 3 depths, from the surface to
the base of the euphotic zone, during Spring (March 1996) and Summer (July
1996). Pigments were analyzed using HPLC for the total water sample and
for the < 8 micrometer size fraction. CHEMTAX (Mackey et al., 1996), a
factor analysis computer program, was used to examine phytoplankton
community structure using marker pigments to determine the relative
importance of various taxa. In addition, we used stepwise multiple linear
regression techniques relating chlorophyll a and marker xanthophyll
pigments as a second approach. Initial applications indicate that both
approaches yielded similar results. In March, whole water samples were
dominated by diatoms, with consistent contributions from dinoflagellates
and cryptophytes. The < 8 micrometer fraction was dominated by small
diatoms, chrysophytes, cryptophytes and dinoflagellates. In Summer,
diatoms were still present and important, but prymnesiophytes,
cryptophytes and cyanobacteria contributed in both size classes. |
| |
| Back to
Biogenic Elements |
| |
| Verity, P, G, Skidaway
Institute of Oceanography, 10 Ocean Science Circle, Savannah, GA
31411, USA, peter@skio.peachnet.edu |
| Redalje, D, G, Dept. of Marine Science,
University of Southern Missippi, Stennis Space Center, MS 39529-0001, USA, donald.redalje@usm.edu |
| Lohrenz, S, E, Dept. of Marine Science,
University of Southern Missippi, Stennis Space Center, MS 39529-0001, USA, steven.lohrenz@usm.edu |
| Paffenhofer, G, A, Skidaway Institute of
Oceanography, 10 Ocean Science Circle, Savannah, GA 31411, USA, cmp@skio.peachnet.edu |
|
| COUPLING BETWEEN PRIMARY PRODUCTION AND PELAGIC
CONSUMPTION IN TEMPERATE OCEAN MARGIN PELAGIC ECOSYSTEMS |
|
| Three fates potentially consume primary production:
portions can be oxidized within the water column, portions can sediment to
shelf/slope depots, and portions can be exported to the interior ocean.
Zooplankton mediate these events. During DOE- and NSF-sponsored studies on
the Mid and South Atlantic Bight shelves, we determined the role of
microzooplankton in these processes. Abundance, composition, and biomass
were determined using an quasi-automated imaging cytometry system. Grazing
and growth rates were measured during dilution incubation experiments
using chlorophyll a as a proxy for phytoplankton biomass. Primary
production (PP), measured as C-14 uptake, was generally 0.5-1.0 gC/m2/d in
spring and 0.5-2.0 in summer. Typically, one-half or more of PP was
contributed by <8um cells. Averaged over time and space,
microzooplankton grazed 57% of chlorophyll a production. Chlorophyll
production, the <8:total fraction of chlorophyll standing stock, and
microzooplankton grazing impact all increased with increasing temperature.
These data indicate that, contrary to traditional paradigms about shelf
ecosystems, small autotrophs contributed the majority of production, and
that this carbon was actively incorporated into the microbial food web. |