This dataset contains the traditional and effective nitrate, phosphate, and silicate fluxes in Lombok, Ombai, and Timor passages, Indian Ocean. Fluxes are depth-resolved and cross-strait integrated, for the 2004-2006 time period of the INSTANT field program. In some cases depths extend below the functional sill depths, due to the moorings being in deeper water. Negative fluxes are westward, towards the Indian Ocean. Files are in self-describing netCDF format, as follows: (1) lombok_trad.nc. Traditional nutrient fluxes for Lombok Strait. (2) lombok_eff.nc. Effective nutrient fluxes for Lombok Strait. (3) ombai_trad.nc. Traditional nutrient fluxes for Ombai Strait. (4) ombai_eff.nc. Effective nutrient fluxes for Ombai Strait. (5) timor_trad.nc. Traditional nutrient fluxes for Timor Passage. (6) timor_eff.nc. Effective nutrient fluxes for Timor Passage.

We compare the formulation and emergent dynamics of 11 CMIP6 IPCC marine biogeochemical models. We find that the largest source of uncertainty across model simulations of marine carbon cycling is grazing pressure (i.e. the phytoplankton specific loss rate to grazing). Variability in grazing pressure is driven by large differences in zooplankton specific grazing rates, which are not sufficiently compensated for by offsetting differences in zooplankton specific mortality rates. Models instead must tune the turnover rate of the phytoplankton population to balance large differences in top-down grazing pressure and constrain net primary production. We then run a controlled sensitivity experiment in a global, coupled ocean-biogeochemistry model to test the sensitivity of marine carbon cycling to this uncertainty and find that even when tuned to identical net primary production, export and secondary production remain extremely sensitive to grazing, likely biasing predictions of future climate states and food security.

This file contains data and associated R code for producing the figures, tables and analysis/models within the manuscript Ferderer et al., Carbonate chemistry fitness landscapes inform diatom resilience to future perturbations. Data was collected at IMAS by Aaron Ferderer.

Ocean alkalinity enhancement (OAE) is an emerging carbon dioxide removal (CDR) strategy that leverages the natural processes of weathering and acid neutralisation to durably store atmospheric CO2 in seawater. OAE can be achieved with a variety of methods, all of which have different environmental implications. One widely considered method utilizes electrochemistry to remove strong acid from seawater, leaving sodium hydroxide (NaOH) behind. This study evaluates the impacts of OAE via NaOH (NaOH-OAE) on a coastal plankton bloom, with particular focus on how macronutrient regeneration in the aftermath of the bloom responds to the perturbation. To investigate this, we enclosed a natural coastal phytoplankton community, including coccolithophores, in nine microcosms. The microcosms were divided into three groups: control, unequilibrated (512.1 ± 2.5 µmol kg-1 alkalinity increase) and equilibrated (499.3 ±5.65 µmol kg-1 alkalinity increase). Light was provided for 11 days to stimulate a bloom (light phase) and lights were turned off thereafter to investigate alkalinity and nutrient changes for 21 days (dark phase). We found no detectable effect of equilibrated NaOH-OAE on phytoplankton community and bacteria abundances determined with flow cytometry but observed a small yet detectable restructuring of phytoplankton communities under unequilibrated conditions. NaOH-OAE had no significant effect on alkalinity, NOx- and phosphate regeneration, but increased silicate regeneration by 64% over 21 days under darkness in the unequilibrated treatments where seawater pH was highest (8.65 relative to 7.92 in the control). Additional dissolution experiments with two diatom species supported this outcome on silicate regeneration for one of the two species, thereby suggesting that the effect is species specific. Our results point towards the potential of NaOH-OAE to influence regeneration of silicate in the surface ocean and thus the growth of diatoms, at least under the very extreme NaOH-OAE conditions simulated here.

During the RV Investigator Eddy voyage (IN2016_V02), we sampled a mesoscale cyclonic and anticyclonic eddy in the Southern Ocean south to Tasmania. We have collected water samples to analyse concentration of phytoplankton biomass and nutrients.

The effect of ocean alkalinity enhancement on a coastal phytoplankton community was assessed via a microcosm experiment. The effect of alkalinity enhancement in two scenarios (i) when enclosed seawater was in equilibrium with atmospheric CO2 and (ii) when enclosed seawater was not in equilibrium with atmospheric CO2 were explored. Alkalinity was increased by ~497 umol/kg in these two treatments and plankton communities, carbonate chemistry, dissolved inorganic nutrients, particulate matter and chlorophyll a dynamics monitored over a 22 day period where a spring bloom occurred.