Areas of Research Interest

Southern Ocean: Biogeochemistry Then and Now

The Southern Ocean plays an outsized role in the Earth’s carbon cycle and climate system. Southern Ocean based research in the Biogeochemistry and Paleoceanography Lab focuses on evaluating surface ocean nutrient dynamics, how they are recorded by sedimenting particles, and how the system has varied in the past. Our goals are to reconstruct surface ocean conditions, to identify linkages to physical and biological processes globally, and use them to improve our understanding of climate and nutrient distribution changes, globally.

Modern Investigations: Constraining how the nitrogen isotopic signature of surface processes are recorded, preserved, and transformed during sinking and sedimentation.

  • Latitudinal transect observations of dissolved and particulate nitrogen to track how nutrient uptake signatures are incorporated into particles
  • Vertical profiles of particulate matter to trace the signal into the sediments
  • Diatom grow-outs to study how the signature is recorded in natural and model systems, examining variability between communities and species, respectively. (Spotlight on Colin Jones)
  • Examining the potential role of diatom resting spores to bias nutrient reconstructions using laboratory cultures. (Spotlight on Isabel Dove)

⇒ Much of this work was conducted in collaboration with the Brzezinski Laboratory at UCSB and the Reisselman Laboratory at U Otago.

◈ Past and present funding for this work is from NSF-PLR and NSF-MGG.

For more information:

Large volume McLane pumps were used to collect particle samples from the upper water column. Here Pat Kelly is shown starting the pumps just prior to deployment on a spectacular day in the Southern Ocean (photo credit: M. Garnsworthy).
Photomicrograph of Thalassiosira lentiginosa from the Sabrina Coast, light microscope 1000x.
SEM photo taken by Isabel Dove and Sarah Kachovich on the JR100.
SEM photo taken by Isabel Dove and Sarah Kachovich on the JR100.
Photomicrograph of Fragilariopsis kerguelensis from the Sabrina Coast, light microscope 1000x.
Photomicrograph of Fragilariopsis kerguelensis from the Sabrina Coast, light microscope 1000x.
Surface ocean particle and surface sediment d15Nbulk v. d15NDB data from a transect of the Southern Ocean along 170°W. The decrease in d15N toward the north in the surface particle data is due to summertime availability and uptake of NH4+ and NO3. The impact of NH4+ uptake appears to be more important for the d15Nbulk values than d15NDB, suggesting that non-diatom phytoplankton were growing on NH4+ preferentially to NO3. The trend in the sediments, with an increase in d15N with latitude, is consistent with an integrated annual uptake of nitrate, with a progressive increase in d15N of nitrate across the Southern Ocean toward the subtropics. In either case, the d15Nbulk v. d15Ndb relationship is not 1:1, where d15NDB tends to increase more steeply toward the north than the d15Nbulk values. The origin of this trend is unknown and a topic of future research.

What is the spatial variability of nutrient consumption and role of the biological pump around the Southern Ocean?

  • What are the respective roles of nutrient supply and physical overturning and nutrient demand related to iron fertilization in driving glacial-interglacial CO2 change?
  • From the vantage point of the Subtropical Front south of Africa: how has the Southern Ocean expanded and contracted over the last 1.5 Ma? (spotlight on GS Basia Marcks)
  • How has nutrient supply, via CDW, varied on the Antarctic Peninsula during the Holocene? (Spotlight on GS Colin Jones, with support from IODP Schlanger Fellowship)

⇒ In collaboration with the Brzezinski Laboratory at UCSB and the Burke Laboratory at University of Notre Dame.

◈ Funding for this work from NSF-PLR and NSF-MGG and USSSP-IODP Exp. 361.

Low latitude and margin biogeochemistry

The low latitudes tend to be nutrient poor and they rely on the supply of nutrients in the subsurface from high latitudes and the delivery of these nutrients to the surface ocean via mixing and upwelling processes. Oxygen also enters the subsurface at high latitudes and is consumed by the products of this low latitude production. We investigate the nutrient supply and demand processes and their interactions with the global distribution of oxygen in the ocean.

What are the roles of nutrient and oxygen delivery and upwelling in regulating large scale changes in biological production and oxygen demand in the low latitudes?

  • Did high latitude nutrient supply regulate export production in the eastern equatorial Pacific over the last 3 Ma?
  • What are the respective roles for oxygen supply from high altitudes versus oxygen regional oxygen demand in regulating variations in water column denitrification in the eastern tropical Pacific?

⇒ In collaboration with Philippe Martinez and Johan Etourneau (U Bordeaux); JR100.

◈ Funding for this work from NSF-MGG.

Coastal Biogeochemistry

Nitrogen additions from human activities have dramatically altered the chemistry and ecology of coastal systems. Our work seeks to identify the key pathways of nitrogen addition and trace the impacts throughout Narragansett Bay and into the nearshore shelf waters.

  • Are distinct nitrogen sources to coastal systems traceable using stable nitrogen isotopes and what other processes are acting to erase these signatures?
  • What is the role of hypoxia in regulating benthic nutrient fluxes?

⇒ In collaboration with Jenkins Lab at URI-CELS.

  • What is the magnitude and distribution of groundwater nutrient inputs to Narragansett Bay?
    • Southern Rhode Island salt ponds
    • Greenwich Bay

⇒ In collaboration with King, Hashemi, Pradhanang Labs at URI and Peterson and Viso Labs at Coastal Carolina University.

◈ Funding for this work from RI Sea Grant, EPA-SNEP Watershed Grants, and RI C-AIM (NSF).

URI undergraduate students Kayly Pelagalli and Samantha Hicks sample groundwater.
URI undergraduate students Kayly Pelagalli and Samantha Hicks sample groundwater.