products as a way of unifying the measurement and analysis teams towards the
answering of the EXPORTS questions. It is likely that a central organization will need to
oversee their construction and dissemination, which will probably be a task for the
EXPORTS project office.
Export Flux - Each EXPORTS deployment needs a synthesized data set of export flux
and vertical flux attenuation for each of the major constituents (POC, PIC, opal, etc.).
This includes determinations of the component fluxes (mass, POC, PIC, opal, etc.) from
the base of the euphotic and at fixed depths (for example 150, 300 & 500 m). Estimates
are needed for each sampling epoch within each sampling cruise and if possible they
will temporally resolve change within each EXPORTS cruise. Export data can be
assembled by several means including sediment traps, biogeochemical mass budgets
Th, etc.), autonomous optical flux proxies, etc. Importantly, each of
the five export pathways (sinking of intact phytoplankton, aggregates or zooplankton
byproducts, vertical submesoscale advection & active vertical migration) needs
quantification. The EXPORTS sampling will be extended through a thorough combing of
the literature to assess additional states.
Productivity - The Productivity data product is needed to address the efficiency of
transfer of net primary production (NPP) to export – the so-called e-ratio (=export/NPP).
This means that estimates of NPP are needed for each sampling epoch where export
data products are available. NPP can come from many measurements (see Table 1).
Export production, new production, and net community production will be measured
Th and tracer mass balances (O
) determined from the shipboard
underway water, autonomous instrumentation or from pumped water from a towed
instrument. Primary production rates will be determined using in situ
incubation method and via the combination of measured phytoplankton carbon biomass
and division rates. By combining estimates of export production with primary production,
we can obtain estimates of the e-ratio.
Plankton Community Structure - Assessment of the phytoplankton and zooplankton
community structure is needed from the surface waters of each deployment. Here, a
summary of abundances by group, and if possible by species, and their vertical
distributions is required. Estimates of the horizontal variability also need to be made
following the mixed layer drifter. Data will come from net tows, in situ imaging, flow and
imaging cytometers, chemotaxonomic phytoplankton pigment, absorption spectra,
genomics, etc. Estimates from satellite ocean color remote sensing of phytoplankton
functional types and size spectra will also be incorporated, especially for understanding
the horizontal and temporal variability at the sites.
Shipboard surveys using underway flow cytometry and imaging techniques as well as
towed camera systems will be used to determine the spatial variability in phytoplankton,
zooplankton and aggregates. The shipboard measurements will be used to develop and
tune optical and acoustical proxies that will then be used from autonomous platforms.
Particle Size Spectra - A data set combining size spectra and changes to the size
spectrum with depth, combined with co-occurring information on community
composition and water column physical characteristics will be analyzed. Particle sizes
range from bacteria (0.5 µm) to sinking aggregates and mesozooplankton (~10’s mm).
This will allow for the study, from surface to mesopelagic, of biological and physical
processes affecting aggregation and disaggregation and their impact on export flux.
Aggregate Aggregation / Disaggregation Rates - Rates will be quantified through
laboratory measurements of (physical and biological) disaggregation of marine particles,
including rates and daughter size spectra, for different types of marine particles.
Temporal variation in particle size spectra may also serve as a proxy measure of
mesopelagic fragmentation/ aggregation processes.
Meso- and Submesoscale Physical and Biogeochemical Mapping - Submesoscale
variations in temperature, salinity and velocity will be measured using ship-based
profilers and autonomous platforms. These will be merged with satellite altimetry
measurements to map the physical variability and tune submesoscale models of this
variability. Detailed measurements of macro- and micro-nutrients will be similarly made
from the ships with a small subset (O
, pH, CO
) made from the autonomous
platforms. Mesoscale budgets of particulate and dissolved organic carbon, oxygen and
other relevant biogeochemical metrics following the time-series mixed layer float will be
assessed. Here we aim to examine the 4-D changes in organic carbon, dissolved
oxygen, etc. following the mixed layer float. Data for this will come from the Lagrangian
and Spatial ships as well as the autonomous assets that are deployed in the study. The
Biogeochemical Budget data product will include all raw data, including the conversion
of electronic signals to biogeochemical parameters, as well as objectively mapped fields
of the same quantities (including error maps). It is also noted that high-resolution
submesoscale surveys will also be needed to evaluate the role of submesoscale vertical
motions on the biological pump (SQ1D; see more details below).
Partitioning of Organic Matter - Field measurements of POM and DOM
concentrations allow for the calculations of net organic matter production and
partitioning over the course of each field campaign. In addition direct measurements of
organic matter production and partitioning between particulate and dissolved phases will
be resolved with shipboard experiments conducted during the process study cruises.
Measurements of particulate inorganic carbon (PIC) and biogenic silica and their rates
of formation are also important for assessments of mineral ballasting. Rate of
particulate primary production as well as extracellular release rates will be measured
directly for each primary production measurement. Rates of DOM production by meso-
and microzooplankton will be measured directly in ship-based experiments conducted
during varying ecosystem and carbon cycling states.
Field measurements of POM and DOM inventories as well as shipboard measurements
of DOM production rates via primary production, micro and macrozooplankton and
microbial conversion of POM to DOM via enzymatic solubilization will be measured in
both the euphotic and mesopelagic zones on each cruise to assess the magnitude of
organic matter partitioning. Field measurements of DOM and POM stocks over the
seasonal time scale will be useful for constraining the seasonal scale advective export
pathway. Subsequent microbial bioavailability assays as well as chemical
characterization of DOM will be required to assess if the resulting DOM is rapidly used
biologically or if it is resistant to decay, accumulates, and potentially available to export
Solubilization, Grazing and Remineralization - Microbial production will be measured
directly from all casts conducted in the field campaigns to determine how they change in
time and space (depth and geographic space). Shipboard experiments will be
conducted to determine the availability of DOM to microbes on time scales of days to
weeks. These data will provide essential estimates of growth efficiency needed to
estimate resource demand imposed by heterotrophic bacterioplankton growth and their
associated remineralization rates. Both shipboard measurements and literature
size/weight-temperature based algorithms of microbial metabolism and zooplankton
grazing and metabolism will be utilized. The solubilization of POM to DOM will be
assessed by measuring particle associated ectoenzyme activity rates in shipboard
experiments. The remineralization of sinking particles will also be measured directly
through tracer experiments and by mass balance experiments in which changes in
organic matter and respiratory gasses are measured directly.
Optics - The link to satellite remote sensing is central to EXPORTS. All EXPORTS
measurements will be conducted alongside measurements of remote sensing
reflectance spectra optimally with a spectral range and resolution similar to that planned
for the PACE mission (350-900 nm at 5 nm resolution; PACE SDT, 2012). These
measurements may be made from free-fall profilers deployed from the ship, using
above water spectroradiometers or another deployment strategy. Inherent optical
properties (IOP’s) are the path from ocean color reflectance to biogeochemistry and
spectral measurements of the absorption, scattering and backscattering will be
assembled. Absorption will be partitioned into dissolved (CDOM) and detrital and
phytoplankton absorption spectra. A similar partition will occur for the scattering and
backscattering spectra. Special efforts will be made to measure IOP’s in the ultraviolet
spectral range, whose remote sensing is a feature of the PACE mission. The IOP
measurements too may come from a suite of autonomous and ship-borne platforms.
There are of course many more possibilities for data products that are needed to
support EXPORTS science goals.
It is absolutely critical that the EXPORTS Science Plan answers the science questions
posed previously. This section details how the EXPORTS field / satellite observational
and numerical program will answer the EXPORTS science questions.
The first high-level science question…
SQ1: How do upper ocean ecosystem characteristics determine the vertical
transfer of organic matter from the well-lit surface ocean?
… has four associated sub-questions. The purpose of the four sub-questions is to
provide facts that contribute to answering the high-level science question. The sub-
questions are obviously interrelated where often one will logically lead to the following.
For example, the first two sub-questions for high-level question one are…
SQ1A: How does plankton community structure regulate the export of organic
matter from the surface ocean?
SQ1B: How do the five pathways that drive export (cf., sinking of intact
phytoplankton, aggregates or zooplankton byproducts, vertical
submesoscale advection & active vertical migration) vary with plankton
These two sub-questions relate export efficiency (SQ1A) and the five export pathways
(SQ1B) to plankton community structure. Understanding the relationship between
plankton community structure and export is central to the goals of the EXPORTS
program. SQ1A focuses on links between plankton community structure and the
efficiency of export of organic matter, defined as the flux of organic carbon leaving the
surface ocean normalized to the rate of NPP in the surface ocean. Export efficiency is
linked to plankton community structure through phytoplankton size, its role in
contributing to export flux via intact phytoplankton composition (e.g. silica and calcite
containing phytoplankton), the phytodetritus contribution to aggregates, the structure of
the zooplankton community and its role in creating fecal pellets, active transport of
carbon to depth via vertical migration, sinking of carcasses and fecal-dominated
aggregates, and the role that phytoplankton community composition has on export.
SQ1B asks how the five export pathways described in figure 3 are related to plankton
community structure. As denoted in figure 3, the relative importance of all three sinking
particle paths (A; sinking phytodetritus, zooplankton byproducts, or aggregates) and the
active transport by vertical migration (C) export pathways will clearly be functions of the
phytoplankton and zooplankton community structure. More subtly, the vertical mixing
and/or advection of suspended organic carbon pathway (B) should also vary with
plankton community structure as surface layer food-web processes create the vertical
differences in suspended organic carbon that are mixed and/or advected to depth.
Details of how the active vertical migration and advective pathways are addressed are
presented in answers to question 2 and sub-question 1D below.
The EXPORTS field program will collect data on both plankton community composition
(both phytoplankton and zooplankton) and export from the surface ocean by several
means aimed at answering Sub-Questions 1A and 1B. The EXPORTS field campaign
will create integrated data products for Export, as well as Plankton Community
Structure and Productivity needed to answer SQ1A (as described in Section 5.7).
Quantification of the relative export pathways (part of the Export data product) is
needed to answer SQ1B. The four EXPORTS field deployments will provide as many
as eight complete snapshots of the ecosystem / carbon cycling state. The collection
and analysis of these states will be the major observational effort in EXPORTS. The
intensive EXPORTS field campaigns will be supplemented by data mining activities that
should provide additional states for our analyses.
To answer SQ1A, we will compare data products for Export, Plankton Community
Structure and Productivity statistically. This work will provide parameterizations
linking community structure and export and will be used as the basis for building and
testing quantitative models, both analytical and statistical, for answering the question of
how plankton community structure sets the magnitude and efficiency of export. The
Productivity data product is needed to help address the efficiency question. Emphasis
will be placed on how plankton community structure, not just total biomass or its
productivity, regulates the export of organic matter from the surface ocean.
To answer SQ1B we will compare how the export pathways will vary as a function of
plankton community structure statistically and use this understanding to build numerical
models to test how the various export pathways change.
The Export and Plankton Community Structure integrated data products will also be
used to test (and hopefully improve) existing satellite ocean color algorithms and
ecological-biogeochemical models. These parameterizations are central for assessing
the export of NPP energy from the upper ocean on global scales and for predicting the
future states of the biological communities that control carbon production, export and
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