FOCI-MOPS v1 – Integration of Marine Biogeochemistry within the Flexible Ocean and Climate Infrastructure version 1 (FOCI 1) Earth system model

The consideration of marine biogeochemistry is essential for simulating the carbon cycle in an Earth system model. Here we present the implementation and evaluation of a marine biogeochemical model, Model of Oceanic Pelagic Stoichiometry (MOPS) in the Flexible Ocean and Climate Infrastructure (FOCI) climate model. FOCI-MOPS enables the simulation of marine biological processes, the marine carbon, nitrogen and oxygen cycles, air-sea gas exchange of CO2 and O2, and simulations with prescribed atmospheric CO2 or CO2 emissions. A series of experiments covering the historical period (1850–2014) were performed following the DECK (Diagnostic, Evaluation and Characterization of Klima) and CMIP6 (Coupled Model Intercomparison Project 6) protocols. Overall, modelled biogeochemical tracer distributions and fluxes, as well as transient evolution in surface air temperature, air-sea CO2 fluxes, and changes of ocean carbon and heat, are in good agreement with observations. Modelled inorganic and organic tracer distributions are quantitatively evaluated by statistically-derived metrics. Results of the FOCI-MOPS model, also including sea surface temperature, surface pH, oxygen (100–600 m), nitrate (0–100 m), and primary production, are within the range of other CMIP6 model results. Overall, the evaluation of FOCI-MOPS indicates its suitability for Earth climate system simulations.

Aerobic Bacteria Produce Nitric Oxide via Denitrification and Trigger Algal Population Collapse

Microbial interactions govern marine biogeochemistry. These interactions are generally considered to rely on exchange of organic molecules. Here we report on a novel inorganic route of microbial communication, showing that algal-bacterial interactions are mediated through inorganic nitrogen exchange. Under oxygen-rich conditions, aerobic bacteria reduce algal-secreted nitrite to nitric oxide (NO) through denitrification, a well-studied anaerobic respiration mechanism. Bacteria secrete NO, triggering a cascade in algae akin to programmed cell death. During death, algae further generate NO, thereby propagating the signal in the algal population. Eventually, the algal population collapses, similar to the sudden demise of oceanic algal blooms. Our study suggests that the exchange of denitrification intermediates, particularly in oxygenated environments, is an overlooked yet ecologically significant route of microbial communication within and across kingdoms.

Genomic evidence for inter-class host transition between abundant streamlined heterotrophs by a novel and ubiquitous marine Methylophage

The methylotrophic OM43 clade are Gammaproteobacteria that comprise some of the smallest free-living cells known with highly streamlined genomes. OM43 represents an important microbial link between marine primary production and return of carbon back to the atmosphere. Bacteriophages shape microbial communities and are major drivers of mortality and global marine biogeochemistry. Recent cultivation efforts have brought the first viruses infecting members of the OM43 clade into culture. Here we characterize a novel myophage infecting OM43, called Melnitz. Melnitz was isolated independently on three separate occasions (with isolates sharing >99.95% average nucleotide identity) from water samples from a subtropical ocean gyre (Sargasso Sea) and temperate coastal (Western English Channel) systems. Metagenomic recruitment from global ocean viromes confirmed that Melnitz is globally ubiquitous, congruent with patterns of host abundance. Bacteria with streamlined genomes such as OM43 and the globally dominant SAR11 clade use riboswitches as an efficient method to regulate metabolism. Melnitz encodes a two-piece tmRNA (ssrA), controlled by a glutamine riboswitch, providing evidence that riboswitch use also occurs for regulation during phage infection of streamlined heterotrophs. Virally encoded tRNAs and ssrA found in Melnitz were phylogenetically more closely related to those found within the alphaproteobacterial SAR11 clade and their associated myophages than those within their gammaproteobacterial hosts. This suggests the possibility of an ancestral inter-class host transition event between SAR11 and OM43. Melnitz and a related myophage that infects SAR11 were unable to infect hosts of the SAR11 and OM43, respectively, suggesting host transition rather than a broadening of host range.

Oceanographic regional climate projections for the Baltic Sea until 2100

Recently performed scenario simulations for the Baltic Sea including marine biogeochemistry were analyzed and compared with earlier published projections. The Baltic Sea, located in northern Europe, is a semi-enclosed, shallow and tide-less sea with seasonal sea ice cover in its northern sub-basins and a long residence time causing oxygen depletion in the bottom water of the southern sub-basins. With the help of dynamical downscaling using a regional coupled atmosphere-ocean climate model, four global Earth System Models were regionalized. As the regional climate model does not include components for the terrestrial and marine biogeochemistry, an additional catchment and coupled physical-biogeochemical model for the Baltic Sea were used. In addition to previous scenario simulations, the impact of various water level scenarios was examined as well. The projections suggest higher water temperatures, a shallower mixed layer with sharper thermocline during summer, reduced sea ice cover and intensified mixing in the northern Baltic Sea during winter compared to present climate. Both frequency and duration of marine heat waves would increase significantly, in particular in the coastal zone of the southern Baltic Sea (except in regions with frequent upwelling). Due to the uncertainties in projections of the regional wind, water cycle and global sea level rise, robust and statistically significant salinity changes cannot be identified. The impact of changing climate on biogeochemical cycling is considerable but in any case smaller than the impact of plausible nutrient input changes. Implementing the proposed Baltic Sea Action Plan, a nutrient input abatement plan for the entire catchment area, would result in a significantly improved ecological status of the Baltic Sea and reduced hypoxic area also in future climate, strengthening the resilience of the Baltic Sea against anticipated future climate change. While our findings about changes in variables of the heat cycle mainly confirm earlier scenario simulations, earlier projections for salinity and biogeochemical cycles differ substantially because of different experimental setups and different bioavailable nutrient input scenarios. During the time in which this paper was prepared, shortly before submission, Christian Dieterich passed away (1964–2021). This sad event marked the end of the life of a distinguished oceanographer and climate scientist who made important contributions to the climate modeling of the Baltic Sea, North Sea and North Atlantic regions.

Southwest Pacific Paleoceanography During the Late Holocene: 3000 years of ocean circulation and marine biogeochemistry reconstructed from New Zealand deep-sea black corals

<p>The global climate results from interactions between the ocean and atmosphere. Ocean gyres are perhaps one of the most significant interactions; they regulate temperature, salinity and nutrient flow across the ocean basins. Gyres transport warm, tropical waters to higher latitudes and cold waters to lower latitudes and act as the dominant heat-transport mechanism in the Earth’s climate system. They also influence spatial patterns in marine primary production by distributing nutrients between the equator and poles. However, gyre circulation in the subtropics has been strengthening, leading to marine heat waves, changing biogeochemistry and reducing primary production since the early 1900s. These changes are often interpreted as a consequence of anthropogenic climate change. However, ocean circulation and primary production can exhibit natural variations on a variety of timescales. Could these recent changes be a part of a long-term natural cycle or a product of anthropogenic change? </p> <b>This research aims to reconstruct South Pacific Gyre (SPG) circulation and biogeochemistry using a suite of New Zealand black corals. The primary research goal is determining if there is a precedent for the ocean changes observed over the instrumental period. Black corals are an ideal paleoceanographic archive for this work; they provide high-resolution, multi-millennial records of biogeochemistry and ocean circulation within their skeletons, derived using radiocarbon (14C) and stable isotopes (d13C and d15N). In this thesis, I show that late Holocene SPG strength has been highly variable and the relationship between circulation and biogeochemistry is timescale dependent. </b><p>The black coral radiocarbon records suggest late Holocene SPG circulation has been controlled by westerly wind strength. Our records show the SPG exhibits natural variability on multi-centennial and millennial timescales that corresponds to the variability within the Southern Annular Mode (SAM) and the El Niño-Southern Oscillation (ENSO). The black coral circulation record shows that the modern gyre circulation is not without precedent over the last 3000 years. </p> <p>The black coral d13C and d15N records show significant variability on multi-decadal to multi-centennial timescales. Multi-centennial variability in black coral d13C and d15N appears to be driven by sea surface temperature (SST), nitrogen fixation rates and wind-driven upwelling and is possibly forced by the mean state of the Southern Oscillation Index and ocean circulation strength. A trend in black coral d13C over the last 1500 years also suggests a shift in phytoplankton community structure towards larger and faster growing phytoplankton. These records also reveal a shift in mean coral d13C and d15N between the 0-2000BP and 2000-3000BP period, the latter corresponding to a period of stronger gyre circulation inferred from the radiocarbon records. </p> <p>This work shows that: 1) New Zealand’s black corals are a promising archive for studying paleoceanography; they can extend instrumental ocean records and fill the gap between traditional southwest Pacific paleoceanographic proxy records (tropical corals, sediment cores); 2) SPG circulation has been highly variable over the last 3000 years; circulation is controlled by atmospheric patterns (e.g. SAM) on multi-centennial to millennial timescales; 3) Gyre circulation is only one of many forcing factors on southwest Pacific primary production and marine biogeochemistry; comparisons between the ∆R, d13C and d15N proxies show that variations in SPG biogeochemical patterns and productivity are likely driven by local dynamics such as phytoplankton community structure, SST, upwelling and gyre circulation. Finally, this research demonstrates the key role that a distributed set of deep-sea coral paleoceanographic reconstructions could play in characterizing the dynamical variability in southwest Pacific Ocean circulation, biogeochemistry and primary production. This information is critical for detecting and attributing past and future anthropogenic impacts on the southwest Pacific Ocean. </p>