Kramer Sasha J.

No Thumbnail Available
Last Name
Kramer
First Name
Sasha J.
ORCID
0000-0002-9944-6779

Search Results

Now showing 1 - 4 of 4
  • Working Paper
    EXPORTS Measurements and Protocols for the NE Pacific Campaign
    (NASA STI Program and Woods Hole Oceanographic Institution, 2021-02) Behrenfeld, Michael J. ; Benitez-Nelson, Claudia R. ; Boss, Emmanuel S. ; Brzezinski, Mark A. ; Buck, Kristen N. ; Buesseler, Ken O. ; Burd, Adrian B. ; Carlson, Craig A. ; Cassar, Nicolas ; Cetinić, Ivona ; Close, Hilary G. ; Craig, Susanne E. ; D'Asaro, Eric A. ; Durkin, Colleen A. ; Estapa, Margaret L. ; Fassbender, Andrea ; Fox, James ; Freeman, Scott ; Gifford, Scott M. ; Gong, Weida ; Graff, Jason R. ; Gray, Deric ; Guidi, Lionel ; Halsey, Kim ; Hansell, Dennis A. ; Haëntjens, Nils ; Horner, Tristan J. ; Jenkins, Bethany D. ; Jones, Janice L. ; Karp-Boss, Lee ; Kramer, Sasha J. ; Lam, Phoebe J. ; Lee, Craig M. ; Lee, Jong-Mi ; Liu, Shuting ; Mannino, Antonio ; Maas, Amy E. ; Marchal, Olivier ; Marchetti, Adrian ; McDonnell, Andrew M. P. ; McNair, Heather ; Menden-Deuer, Susanne ; Morison, Francoise ; Nelson, Norman B. ; Nicholson, David P. ; Niebergall, Alexandria K. ; Omand, Melissa M. ; Passow, Uta ; Perry, Mary J. ; Popp, Brian N. ; Proctor, Chris ; Rafter, Patrick ; Roca-Martí, Montserrat ; Roesler, Collin S. ; Rubin, Edwina ; Rynearson, Tatiana A. ; Santoro, Alyson E. ; Siegel, David A. ; Sosik, Heidi M. ; Soto Ramos, Inia ; Stamieszkin, Karen ; Steinberg, Deborah K. ; Stephens, Brandon M. ; Thompson, Andrew F. ; Van Mooy, Benjamin A. S. ; Zhang, Xiaodong
    EXport Processes in the Ocean from Remote Sensing (EXPORTS) is a large-scale NASA-led and NSF co-funded field campaign that will provide critical information for quantifying the export and fate of upper ocean net primary production (NPP) using satellite information and state of the art technology.
  • Article
    Bio-optical discrimination of diatoms from other phytoplankton in the surface ocean: Evaluation and refinement of a model for the Northwest Atlantic
    (Elsevier, 2018-08-15) Kramer, Sasha J. ; Roesler, Collin S. ; Sosik, Heidi M.
    Diatoms dominate global silica production and export production in the ocean; they form the base of productive food webs and fisheries. Thus, a remote sensing algorithm to identify diatoms has great potential to describe ecological and biogeochemical trends and fluctuations in the surface ocean. Despite the importance of detecting diatoms from remote sensing and the demand for reliable methods of diatom identification, there has not been a systematic evaluation of algorithms that are being applied to this end. The efficacy of these models remains difficult to constrain in part due to limited datasets for validation. In this study, we test a bio-optical algorithm developed by Sathyendranath et al. (2004) to identify diatom dominance from the relationship between ratios of remote sensing reflectance and chlorophyll concentration. We evaluate and refine the original model with data collected at the Martha's Vineyard Coastal Observatory (MVCO), a near-shore location on the New England shelf. We then validated the refined model with data collected in Harpswell Sound, Maine, a site with greater optical complexity than MVCO. At both sites, despite relatively large changes in diatom fraction (0.8–82% of chlorophyll concentration), the magnitude of variability in optical properties due to the dominance or non-dominance of diatoms is less than the variability induced by other absorbing and scattering constituents of the water. While the original model performance was improved through successive re-parameterizations and re-formulations of the absorption and backscattering coefficients, we show that even a model originally parameterized for the Northwest Atlantic and re-parameterized for sites such as MVCO and Harpswell Sound performs poorly in discriminating diatom-dominance from optical properties.
  • Article
    Seasonal mixed layer depth shapes phytoplankton physiology, viral production, and accumulation in the North Atlantic
    (Nature Research, 2021-11-17) Diaz, Ben P. ; Knowles, Benjamin ; Johns, Christopher T. ; Laber, Christien P. ; Bondoc, Karen Grace V. ; Haramaty, Liti ; Natale, Frank ; Harvey, Elizabeth L. ; Kramer, Sasha J. ; Bolaños, Luis M. ; Lowenstein, Daniel P. ; Fredricks, Helen F. ; Graff, Jason R. ; Westberry, Toby K. ; Mojica, Kristina D. A. ; Haëntjens, Nils ; Baetge, Nicholas ; Gaube, Peter ; Boss, Emmanuel S. ; Carlson, Craig A. ; Behrenfeld, Michael J. ; Van Mooy, Benjamin A. S. ; Bidle, Kay D.
    Seasonal shifts in phytoplankton accumulation and loss largely follow changes in mixed layer depth, but the impact of mixed layer depth on cell physiology remains unexplored. Here, we investigate the physiological state of phytoplankton populations associated with distinct bloom phases and mixing regimes in the North Atlantic. Stratification and deep mixing alter community physiology and viral production, effectively shaping accumulation rates. Communities in relatively deep, early-spring mixed layers are characterized by low levels of stress and high accumulation rates, while those in the recently shallowed mixed layers in late-spring have high levels of oxidative stress. Prolonged stratification into early autumn manifests in negative accumulation rates, along with pronounced signatures of compromised membranes, death-related protease activity, virus production, nutrient drawdown, and lipid markers indicative of nutrient stress. Positive accumulation renews during mixed layer deepening with transition into winter, concomitant with enhanced nutrient supply and lessened viral pressure.
  • Article
    An operational overview of the EXport Processes in the Ocean from RemoTe Sensing (EXPORTS) Northeast Pacific field deployment
    (University of California Press, 2021-07-07) Siegel, David A. ; Cetinić, Ivona ; Graff, Jason R. ; Lee, Craig M. ; Nelson, Norman B. ; Perry, Mary J. ; Soto Ramos, Inia ; Steinberg, Deborah K. ; Buesseler, Ken O. ; Hamme, Roberta C. ; Fassbender, Andrea ; Nicholson, David P. ; Omand, Melissa M. ; Robert, Marie ; Thompson, Andrew F. ; Amaral, Vinicius ; Behrenfeld, Michael J. ; Benitez-Nelson, Claudia R. ; Bisson, Kelsey ; Boss, Emmanuel S. ; Boyd, Philip ; Brzezinski, Mark A. ; Buck, Kristen N. ; Burd, Adrian B. ; Burns, Shannon ; Caprara, Salvatore ; Carlson, Craig A. ; Cassar, Nicolas ; Close, Hilary G. ; D'Asaro, Eric A. ; Durkin, Colleen A. ; Erickson, Zachary K. ; Estapa, Margaret L. ; Fields, Erik ; Fox, James ; Freeman, Scott ; Gifford, Scott M. ; Gong, Weida ; Gray, Deric ; Guidi, Lionel ; Haëntjens, Nils ; Halsey, Kim ; Huot, Yannick ; Hansell, Dennis A. ; Jenkins, Bethany D. ; Karp-Boss, Lee ; Kramer, Sasha J. ; Lam, Phoebe J. ; Lee, Jong-Mi ; Maas, Amy E. ; Marchal, Olivier ; Marchetti, Adrian ; McDonnell, Andrew M. P. ; McNair, Heather ; Menden-Deuer, Susanne ; Morison, Francoise ; Niebergall, Alexandria K. ; Passow, Uta ; Popp, Brian N. ; Potvin, Geneviève ; Resplandy, Laure ; Roca-Martí, Montserrat ; Roesler, Collin S. ; Rynearson, Tatiana A. ; Traylor, Shawnee ; Santoro, Alyson E. ; Seraphin, Kanesa ; Sosik, Heidi M. ; Stamieszkin, Karen ; Stephens, Brandon M. ; Tang, Weiyi ; Van Mooy, Benjamin ; Xiong, Yuanheng ; Zhang, Xiaodong
    The goal of the EXport Processes in the Ocean from RemoTe Sensing (EXPORTS) field campaign is to develop a predictive understanding of the export, fate, and carbon cycle impacts of global ocean net primary production. To accomplish this goal, observations of export flux pathways, plankton community composition, food web processes, and optical, physical, and biogeochemical (BGC) properties are needed over a range of ecosystem states. Here we introduce the first EXPORTS field deployment to Ocean Station Papa in the Northeast Pacific Ocean during summer of 2018, providing context for other papers in this special collection. The experiment was conducted with two ships: a Process Ship, focused on ecological rates, BGC fluxes, temporal changes in food web, and BGC and optical properties, that followed an instrumented Lagrangian float; and a Survey Ship that sampled BGC and optical properties in spatial patterns around the Process Ship. An array of autonomous underwater assets provided measurements over a range of spatial and temporal scales, and partnering programs and remote sensing observations provided additional observational context. The oceanographic setting was typical of late-summer conditions at Ocean Station Papa: a shallow mixed layer, strong vertical and weak horizontal gradients in hydrographic properties, sluggish sub-inertial currents, elevated macronutrient concentrations and low phytoplankton abundances. Although nutrient concentrations were consistent with previous observations, mixed layer chlorophyll was lower than typically observed, resulting in a deeper euphotic zone. Analyses of surface layer temperature and salinity found three distinct surface water types, allowing for diagnosis of whether observed changes were spatial or temporal. The 2018 EXPORTS field deployment is among the most comprehensive biological pump studies ever conducted. A second deployment to the North Atlantic Ocean occurred in spring 2021, which will be followed by focused work on data synthesis and modeling using the entire EXPORTS data set.