I study how biological and physical processes interact to drive biogeochemical cycling in the polar and sub-polar oceans in order to gain a mechanistic understanding that can ultimately aid our ability to predict future responses to and feedbacks on climate change. I take an interdisciplinary approach that combines biological, physical and chemical oceanography while utilizing in situ observations, remote sensing and modeling.
Current Projects
Drivers of the North Atlantic Bloom
The North Atlantic Ocean is home to one of the largest annual phytoplankton blooms in the world. This bloom is not only important ecologically as it forms the base of the food chain, but it also transfers large amounts of carbon from the atmosphere to the deep ocean. While we know it plays a role in global climate, the drivers of this bloom are still hotly debated and hypotheses are evolving as we obtain higher resolution measurements that indicate small scale physical processes can greatly influence the overall magnitude and timing of the bloom at basin scales. I am investigating these links between physics and biology and small and large spatial scales with a geostatistical analysis of a high-resolution ecosystem model in the region. This project is part of the North Atlantic Aerosols and Marine Ecosystems Study (NAAMES).
Completed Projects
Sea ice Heterogeneity
Prior studies in the Western Antarctic Peninsula, including my own, have all relied on relatively coarse remotely-sensed sea ice metrics that mask biologically relevant ice variability including thickness, type, stage of development and dynamic behavior. I am currently filling this gap by using high-resolution satellite imagery and decades of unutilized daily sea ice observations in the field. Once this ice heterogeneity is resolved I will investigate links to biogeochemical and ecosystem variability over the past twenty years with an eye towards enhanced predicative capabilities of future change.
Jeff Schmaltz, NASA
EIMS
One tool in this investigation is an Equilibrator Inlet Mass Spectrometer (EIMS). With this instrument we can measure the oxygen-argon (O2/Ar) ratio underway at unprecedented sub-kilometer spatial resolution. Oxygen records the net metabolic balance between photosynthesis and respiration in the mixed layer, but is also influenced by physical processes such as temperature and salinity driven solubility changes, bubble injection and ice melt-freeze. Argon is affected similarly by these physical processes but is biologically inert. Thus by taking the ratio of O2 to Ar we can isolate the biological component. Together with an estimate of gas exchange we can estimate net community production (NCP) in the mixed layer.
Arctic Ocean
Sea ice extent in the Arctic has rapidly declined in recent decades, while ocean temperatures have warmed, and many have speculated on how an evolving physical landscape may impact productivity. Critical to our prediction of future change in carbon cycling is a thorough understanding of biological-physical couplings today. We employ concurrent measurements of O2/Ar and total O2 to devolve biological oxygen and physical (abiotic) oxygen (Ar) supersaturations. We document net autotrophy in the surface water under ice cover in the upper Arctic Ocean that may increase as ice thins. Physical oxygen is undersaturated in the Nansen Basin as a result of ice melt, Atlantic water influence and/or cooling, while it is supersaturated in the Canadian Basin likely due to net freezing over several seasons.
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Eveleth et al. 2014 is available here
Western Antarctic Peninsula
Two recently published companion papers examine physical drivers of biological signals in the Western Antarctic Peninsula. This region is changing rapidly with one of the fastest warming rates on the planet, shifts in sea ice cover, and impacts on biological activity from the base of the food chain all the way up to the whales and penguins. I participated in the 6 week Palmer LTER research cruise in January 2013 and our lab now has underway O2/Ar data for 2012-2015. These underway measurements reveal substantial small scale variability that is not detected in the traditional station sampling strategy. I document the length scales and magnitudes of the biological oxygen, physical oxygen, pCO2 and NCP variability in the WAP and Drake Passage and then describe the driving mechanisms. A mechanistic understand will help us predict future changes in the area and potential feedbacks on the climate system.
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Eveleth et al. 2017 a (O2/Ar and pCO2) is available here
Eveleth et al. 2017 b (NCP in the WAP) is available here
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