Effects of short-term warming on surface ocean productivity: A case study across nitrogen- to iron-limited waters of the South Atlantic and Southern Ocean

Synergistic effects among ecosystem stressors introduce significant uncertainty in efforts to model biogeochemical climate feedbacks. In theory, future ocean warming should increase metabolic rates, with implications for productivity and biological carbon sequestration; however, nutrient limitation has the potential to severely dampen the realized effects of warming. This study investigated the effects of short-term warming on nutrient acquisition and net community production under distinct nutrient limitation regimes. Seven experiments were carried out across Fe-limited waters of the Southern Ocean to N-limited waters of the South Atlantic gyre. While N plays myriad roles in cells, Fe is used primarily in catalysis, meaning that Fe demand may decrease with warming given gains in enzymatic efficiency. Water was collected using a trace metal-clean sampling approach and incubated at ambient temperature, +2ºC, and +4ºC. At 72 h, ¹⁵N substrates were added to determine nitrate and ammonium uptake rates; endpoint samples were collected at 78 h. We quantified change per degree warming in nutrient and particulate organic carbon/N (POC/PON) concentrations, which generally scaled linearly with temperature. POC and PON increased by 10-30% of standing stock per degree warming in Fe-limited waters south of the Subantarctic Front and in co-limited waters at the Subtropical Front. North of the Subantarctic Front, gains increased by <6% per degree warming. Our results suggest that Fe-limited communities in the Southern Ocean may respond more strongly to warming events, with implications for climate feedbacks associated with the biological carbon pump.

Presentation Preference: Oral

Primary Presenter: Corday Selden, Rutgers University (crselden@marine.rutgers.edu)

Authors:

Corday Selden, Rutgers University  (crselden@marine.rutgers.edu)

Susanna Weiss, Rutgers University  (susweez@gmail.com)

Mark Moore, University of Southampton  (C.M.Moore@soton.ac.uk)

Thomas Ryan-Keogh, Southern Ocean Carbon and Climate Observatory  (tryankeogh@csir.co.za)

Katherine Dawson, Rutgers University  (kat.dawson@rutgers.edu)

Karel Bakker, Royal Netherlands Institute for Sea Research  (karel.bakker@nioz.nl)

Ben Cala, Royal Netherlands Institute for Sea Research  (ben.cala@nioz.nl)

Sarah Le Besque, Oxford University  (sarah.lebesque@sjc.ox.ac.uk)

Joe Furby, University of Southampton  (jf7g18@soton.ac.uk)

Tom Bibby, University of Southampton  (tsb@soton.ac.uk)