Researchers

Eric D'Asaro

Senior Principal Oceanographer

OPD Department

APL-UW

Professor, Oceanography

Craig Lee

Senior Principal Oceanographer

OPD Department

APL-UW

Associate Professor, Oceanography

Jason Gobat

Senior Principal Oceanographer

OPD Department

APL-UW

Mike Ohmart

Field Engineer II

OE Department

APL-UW

Eric Rehm

Predoctoral Research Associate

OPD Department

APL-UW

Amanda Gray

Senior Engineer

EPS Department

APL-UW

Geoff Shilling

Principal Engineer

OPD Department

APL-UW

Adam Huxtable

Engineer IV

OPD Department

APL-UW

Collaborators

Amala Mahadevan

Associate Scientist

Woods Hole Oceanographic Institution

Mary Jane Perry

Professor

University of Maine

Funding

NSF

NASA

North Atlantic Bloom Experiment

Ocean eddies drive early onset of springtime phytoplankton blooms

During the experiment we measured a new physical mechanism, in which eddies take horizontal density gradients and convert them to vertical density gradients. This causes a stratification, that in turn causes more sunlight to reach the phytoplankton, therefore they grow earlier. And that is what is initiating the North Atlantic bloom.

Results Published in Science

More About This Research

Publications
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Particulate organic carbon and inherent optical properties during 2008 North Atlantic Bloom Experiment

Cetinić, I., M.J. Perry, N.T. Briggs, E. Kallin, E.A. D'Asaro, and C.M. Lee, "Particulate organic carbon and inherent optical properties during 2008 North Atlantic Bloom Experiment," J. Geophys. Res., 117, doi:10.1029/2011JC007771, 2012.

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30 Jun 2012

The co-variability of particulate backscattering (bbp) and attenuation (cp) coefficients and particulate organic carbon (POC) provides a basis for estimating POC on spatial and temporal scales that are impossible to obtain with traditional sampling and chemical analysis methods. However, the use of optical proxies for POC in the open ocean is complicated by variable relationships reported in the literature between POC and cp or bbp. During the 2008 North Atlantic Bloom experiment, we accrued a large data set consisting of >300 POC samples and simultaneously measured cp and bbp. Attention to sampling detail, use of multiple types of POC blanks, cross-calibration of optical instruments, and parallel measurements of other biogeochemical parameters facilitated distinction between natural and methodological-based variability. The POC versus cp slope varied with plankton community composition but not depth; slopes were 11% lower for the diatom versus the recycling community. Analysis of literature POC versus cp slopes indicates that plankton composition is responsible for a large component of that variability. The POC versus bbp slope decreased below the pycnocline by 20%, likely due to changing particle composition associated with remineralization and fewer organic rich particles. The higher bbp/cp ratios below the mixed layer are also indicative of particles of lower organic density. We also observed a peculiar platform effect that resulted in ~27% higher values for downcast versus upcast bbp measurements. Reduction in uncertainties and improvement of accuracies of POC retrieved from optical measurements is important for autonomous sampling, and requires community consensus for standard protocols for optics and POC.

Estimates of net community production and export using high-resolution, Lagrangian measurements of O2, NO3, and POC through the evolution of a spring diatom bloom in the North Atlantic

Alkire, M.B., E. D'Asaro, C. Lee, M.J. Perry, A. Gray, I. Cetinic, N. Briggs, E. Rehm, E. Kallin, J. Kaiser, and A. Gonzalez-Posada, "Estimates of net community production and export using high-resolution, Lagrangian measurements of O2, NO3, and POC through the evolution of a spring diatom bloom in the North Atlantic," Deep Sea Res. I, 64, 157-174, doi:10.1016/j.dsr.2012.01.012, 2012.

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1 Jun 2012

Budgets of nitrate, dissolved oxygen, and particulate organic carbon (POC) were constructed from data collected on-board a Lagrangian, profiling float deployed between April 4 and May 25, 2008, as part of the North Atlantic Bloom Experiment. These measurements were used to estimate net community production (NCP) and apparent export of POC along the float trajectory. A storm resulting in deep mixing and temporary suspension of net production separated the bloom into early (April 23–27) and main (May 6–13) periods over which ~264 and ~805 mmol C m-2 were produced, respectively. Subtraction of the total POC production from the NCP yielded maximum estimates of apparent POC export amounting to ~92 and 574 mmol C m-2 during the early and main blooms, respectively. The bloom terminated the following day and ~282 mmol C m-2 were lost due to net respiration (70%) and apparent export (30%). Thus, the majority of the apparent export of POC occurred continuously during the main bloom and a large respiration event occurred during bloom Termination. A comparison of the POC flux during the main bloom period with independent estimates at greater depth suggest a rapid rate of remineralization between 60 and 100 m. We suggest the high rates of remineralization in the upper layers could explain the apparent lack of carbon overconsumption (C:N>6.6) in the North Atlantic during the spring bloom.

Optimizing models of the North Atlantic spring bloom using physical, chemical, and bio-optical observations from a Lagrangian float.

Bagniewski, W., K. Fennel, M.J. Perry, and E.A. D'Asaro, "Optimizing models of the North Atlantic spring bloom using physical, chemical, and bio-optical observations from a Lagrangian float." Biogeosciences, 8, 1291-1307, doi: 10.5194/bg-8-1291-2011, 2011.

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25 May 2011

The North Atlantic spring bloom is one of the main events that lead to carbon export to the deep ocean and drive oceanic uptake of CO2 from the atmosphere. Here we use a suite of physical, bio-optical and chemical measurements made during the 2008 spring bloom to optimize and compare three different models of biological carbon export. The observations are from a Lagrangian float that operated south of Iceland from early April to late June, and were calibrated with ship-based measurements. The simplest model is representative of typical NPZD models used for the North Atlantic, while the most complex model explicitly includes diatoms and the formation of fast sinking diatom aggregates and cysts under silicate limitation. We carried out a variational optimization and error analysis for the biological parameters of all three models, and compared their ability to replicate the observations. The observations were sufficient to constrain most phytoplankton-related model parameters to accuracies of better than 15%. However, the lack of zooplankton observations leads to large uncertainties in model parameters for grazing. The simulated vertical carbon flux at 100 m depth is similar between models and agrees well with available observations, but at 600 m the simulated flux is larger by a factor of 2.5 to 4.5 for the model with diatom aggregation. While none of the models can be formally rejected based on their misfit with the available observations, the model that includes export by diatom aggregation has a statistically significant better fit to the observations and more accurately represents the mechanisms and timing of carbon export based on observations not included in the optimization. Thus models that accurately simulate the upper 100 m do not necessarily accurately simulate export to deeper depths.

Export and mesopelagic particle flux during a North Atlantic spring diatom bloom

Martin, P., R.S. Lampitt, M.J. Perry, R. Sanders, C. Lee, and E. D'Asaro, "Export and mesopelagic particle flux during a North Atlantic spring diatom bloom," Deep Sea Res. I, 58, 338-349, doi: 10.1016/j.dsr.2011.01.006, 2011.

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1 Apr 2011

Spring diatom blooms are important for sequestering atmospheric CO2 below the permanent thermocline in the form of particulate organic carbon (POC). We measured downward POC flux during a sub-polar North Atlantic spring bloom at 100 m using thorium-234 (234Th) disequilibria, and below 100 m using neutrally buoyant drifting sediment traps. The cruise followed a Lagrangian float, and a pronounced diatom bloom occurred in a 600 km2 area around the float. Particle flux was low during the first three weeks of the bloom, between 10 and 30 mg POC m/d. Then, nearly 20 days after the bloom had started, export as diagnosed from 234Th rose to 360-620 mg POC m2/d, co-incident with silicate depletion in the surface mixed layer. Sediment traps at 600 and 750 m depth collected 160 and 150 mg POC m2/ d, with a settled volume of particles of 1000-1500 mL m2/ d. This implies that 25-43% of the 100 m POC export sank below 750 m. The sinking particles were ungrazed diatom aggregates that contained transparent exopolymer particles (TEP). We conclude that diatom blooms can lead to substantial particle export that is transferred efficiently through the mesopelagic. We also present an improved method of calibrating the Alcian Blue solution against Gum Xanthan for TEP measurements.

Convection and the seeding of the North Atlantic bloom

D'Asaro, E.A., "Convection and the seeding of the North Atlantic bloom," J. Mar. Syst., 69, 233-237, doi:10.1016/j.jmarsys.2005.08.005, 2008.

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28 Feb 2008

Observations of vertical velocities in deep wintertime mixed layers using neutrally buoyant floats show that the convectively driven vertical velocities, roughly 1000 m per day, greatly exceed the sinking velocities of phytoplankton, 10 m or less per day. These velocities mix plankton effectively and uniformly across the convective layer and are therefore capable of returning those that have sunk to depth back into the euphotic zone. This mechanism cycles cells through the surface layer during the winter and provides a seed population for the spring bloom. A simple model of this mechanism applied to immortal phytoplankton in the subpolar Labrador Sea predicts that the seed population in early spring will be a few percent of the fall concentration if the plankton sink more slowly than the mean rate at which the surface well-mixed layer grows over the winter. Plankton that sink faster than this will mostly sink into the abyss with only a minute fraction remaining by spring. The shallower mixed layers of mid-latitudes are predicted to be much less effective at maintaining a seed population over the winter, limiting the ability of rapidly sinking cells to survive the winter.

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