1. Hypotheses
Prior results have documented eddy-driven transport
of nutrients into the euphotic zone and the associated accumulation
of chlorophyll. However, several key aspects of mesoscale upwelling events
remain unresolved by the extant database, including: (1) phytoplankton
physiological response, (2) changes in community structure, (3) impact
on export out of the euphotic zone, (4) rates of mixing between the surface
mixed layer and the base of the euphotic zone, and (5) implications for
biogeochemistry and differential cycling of carbon and associated bioactive
elements. This leads to the following hypotheses concerning the complex,
non-linear biological regulation of elemental cycling in the ocean:
H1: Eddy-induced
upwelling, in combination with diapycnal mixing in the upper ocean,
introduces new nutrients into the euphotic zone.
H2: The increase in inorganic nutrients
stimulates a physiological response within the phytoplankton community.
H3: Differing physiological responses
of the various species bring about a shift in community structure.
H4: Changes in community structure
lead to increases in export from, and changes in biogeochemical cycling within,
the upper ocean.
2. Scenarios
There are several scenarios in which this chain
of hypotheses could be linked or broken. These
include, but are not necessarily limited to, the following:
S1: Nutrient input to the euphotic
zone simply increases the rate of production by the background species assemblage
dominated by picoplankton; impacts on biogeochemical cycling are nil.
S2: Increased nitrate availability stimulates
a bloom of diatoms; silica-rich organic material produced in the bloom sinks
rapidly out of the euphotic zone once the nutrients are exhausted.
S3: Shoaling isopycnals transport DIP
closer to the surface, facilitating nitrogen fixation by Trichodesmium
or perhaps vertically migrating diatoms with symbiotic bacteria; nitrogen-rich
organic material produced during the bloom is exported primarily in
dissolved form.
S4: The eddy feature accommodates a
change in community structure and biomass of consumers that produce
rapidly sinking particles.
3. Objectives
The following objectives are designed to test
hypotheses H1-H4 and distinguish between the scenarios
S1-S4 in which the chain of hypotheses are linked or
broken.
O1: Measure
the enhancement of inorganic nutrient availability brought about by
eddy-induced upwelling.
O2: Measure
the phytoplankton physiological response to increased nutrients.
O3: Assess
shifts in species composition associated with the eddy disturbance.
O4: Quantify
the impact of the eddy disturbance on upper ocean biogeochemical cycling:
measure elemental inventories, primary production, and export.
2004
February
Second PI meeting, ASLO/TOS Conference, Honolulu
Summer
Field Work
2005
Winter
PI meeting: analysis of ’04 and planning for
‘05
Summer
Field Work
2006
Winter
PI meeting: synthesis and manuscript preparation
June 30
End date
5. Related Projects and
Proposals
Participation
starting in 2004:
Steinberg
Zooplankton net tows
Davis
VPR
Carlson
prokaryotic community structure and DOM dynamics
Armbrust
genetic diversity in eukaryotes
Oakey/Ledwell Finestructure
Participating
in 2005:
Shipe/Brzezinski
N and Si uptake
Fratantoni
Gliders
Schofield
Gliders
Benitez-Nelson
et al. Hawaiian Eddy Project “EFLUX”
http://www.soest.hawaii.edu/oceanography/eddy/
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