Climate pathways behind phytoplankton-induced atmospheric warming

We investigate the ways in which marine biologically mediated heating increases the surface atmospheric temperature. While the effects of phytoplankton light absorption on the ocean have gained attention over the past years, the impact of this biogeophysical mechanism on the atmosphere is still unclear. Phytoplankton light absorption warms the surface of the ocean, which in turn affects the air–sea heat and CO2 exchanges. However, the contribution of air–sea heat versus CO2 fluxes in the phytoplankton-induced atmospheric warming has not been yet determined. Different so-called climate pathways are involved. We distinguish heat exchange, CO2 exchange, dissolved CO2, solubility of CO2 and sea-ice-covered area. To shed more light on this subject, we employ the EcoGEnIE Earth system model that includes a new light penetration scheme and isolate the effects of individual fluxes. Our results indicate that phytoplankton-induced changes in air–sea CO2 exchange warm the atmosphere by 0.71 ∘C due to higher greenhouse gas concentrations. The phytoplankton-induced changes in air–sea heat exchange cool the atmosphere by 0.02 ∘C due to a larger amount of outgoing longwave radiation. Overall, the enhanced air–sea CO2 exchange due to phytoplankton light absorption is the main driver in the biologically induced atmospheric heating

The Relative Importance of Phytoplankton Light Absorption and Ecosystem Complexity in an Earth System Model

We investigate the relative importance of ecosystem complexity and phytoplankton light absorption for climate studies. While the complexity of Earth System models (ESMs) with respect to marine biota has increased over the past years, the relative importance of biological processes in driving climate-relevant mechanisms such as the biological carbon pump and phytoplankton light absorption is still unknown. The climate effects of these mechanisms have been studied separately, but not together. To shed light on the role of biologically mediated feedbacks, we performed different model experiments with the EcoGENIE ESM. The model experiments have been conducted with and without phytoplankton light absorption and with two or 12 plankton functional types. For a robust comparison, all simulations are tuned to have the same primary production. Our model experiments show that phytoplankton light absorption changes ocean physics and biogeochemistry. Higher sea surface temperature decreases the solubility of CO2 which in turn increases the atmospheric CO2 concentration, and finally the atmospheric temperature rises by 0.45°C. An increase in ecosystem complexity increases the export production of particulate organic carbon but decreases the amount of dissolved organic matter. These changes in the marine carbon cycling, however, hardly reduces the atmospheric CO2 concentrations and slightly decreases the atmospheric temperature by 0.034°C. Overall we show that phytoplankton light absorption has a higher impact on the carbon cycle and on the climate system than a more detailed representation of the marine biota

Short-term dynamics of a high energy embayed beach: Stanwell Park, NSW, Australia

The three-dimensional variability of the subaerial beach is examined for Stanwell Park Beach, New South Wales (NSW), Australia. This embayed environment has previously been studied over long time scales (decades), but not over shorter time scales (days, weeks). Embayed beaches experience rotation events during which opposite accretion and erosion patterns are observed at the extremities of the beach. To analyse this phenomenon, the beach is mapped with 10 Real-Time Kinematic Global Positioning System (RTK-GPS) surveys collected from 10th February 2016 to 14th May 2016. This study aims to examine short-term changes (days, weeks) to the morphology of the subaerial beach of Stanwell Park Beach and any factors that may influence its behaviours. We show that a short-time beach rotation event occurs over one month, caused by a large eastern swell. However, swell with a southern direction generates rip current channels on the subaerial beach face. During this particular event, the amount of sediment transported is lower than during beach rotation events. Furthermore, Stanwell Park Beach has two lagoons that can open to discharge water accumulated in these lagoons. We show that during heavy rainfall, the lagoons open, transporting sediment in surf zone and thus causing erosion. This study provides a clear demonstration of the sensitivity of embayed beaches to short-term variability in wave climate

Argo-based anthropogenic carbon concentration and inventory in the Labrador and Irminger Seas over 2011-2021

Poster.-- EGU General Assembly 2023, Vienna, Austria, 24–28 April 2023.-- This work is distributed under the Creative Commons Attribution 4.0 LicenseThe ocean is a net sink for a quater of the carbon dioxide emitted to the atmosphere by human industrial activities and land-use change (Cant). The North Atlantic Ocean encompasses the highest ocean storage capacity of Cant per unit area. In particular, the Labrador and Irminger Seas are two basins storing a high amount of Cant due to the deep convection activity taking place there. The temporal evolution of Cant concentration in these two basins and their Cant inventories in the 0-1800 depth layer are estimated over the period 2011-2021. The Cant values are estimated from Argo floats equipped with oxygen sensors, predictive neural networks (ESPER_NN and CONTENT) and a carbon-based back-calculation method (φCOT method). On average, Cant inventories are similar in the two basins and amount to 75.3 and 75.6 mol/m2 in the Irminger and Labrador seas, respectively. Over the study period, Cant inventories increase in the two basins at a storage rate of 1.01±0.14 mol/m2/yr in the Irminger Sea and 0.94±0.2 mol/m2/yr in the Labrador Sea. The processes involved in Cant evolution in the two basins are then investigatedN

Intra-annual variability of carbon signature and transport in the North Atlantic Ocean

EGU General Assembly 2023, Vienna, Austria, 24–28 April 2023.-- This work is distributed under the Creative Commons Attribution 4.0 LicenseThe ocean is the largest carbon reservoir on Earth, and a major sink for the excess of CO2 (anthropogenic carbon) emitted to the atmosphere by human activities. Having removed about a quater of these emissions since the beginning of the industrial era, ocean’s key role in climate is particularty outstanding in the North Atlantic (NA). A combination of physical and biological processes makes the NA a key-role region for the natural and anthropogenic carbon uptake and storage, and hence for the global carbon cycle. Traditionally, the seasonal carbon cycle has been assumed to respond to natural variability, unnafected by the ongoing anthropogenic increase of atmospheric CO2. Recent model projections, however, point otherwise, yet observational evidence to verify these predictions is still missing. Here we examine seasonal cycle in dissolved inorganic carbon (DIC) and its (surface-2000 dbar) transport, estimated using in-situ data and neural networks, across the OVIDE (GO-SHIP A25) section, from 1993 to 2021 at a monthly resolution. Our results highlight that changes in temperature, dissolved oxygen and ocean circulation are key components driving the seasonal DIC variability. DIC concentrations are higher in years with strong winter mixing regimes (which bring more nutrient-rich waters to the surface, favouring photosynthesis, and more (remineralized) carbon back to the surface). Seasonal DIC transport fluctuations are found significant compared to the mean (e.g. +/- 25% in the upper branch of the meridional overturning circulation), putting into relevance that caution is needed if assuming that single-cruise occupations are representative of the annual state. We also observe a yearly variant seasonal imbalance, with a significant reduction over the past two decades in the upper branch of the meridional overturning circulation. These results underscore the importance of considering intra-annual variability in the North Atlantic's carbon cycle when addressing climate changeN

Mechanisms controlling the abyssal transport of anthropogenic carbon in the North Atlantic

EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022.-- This work is distributed under the Creative Commons Attribution 4.0 LicenseSince the industrial revolution, human activities have emitted large amount of anthropogenic carbon (Cant) into the atmosphere through the burning of fossil fuel, the production of cement and land-use change. Via air-sea gas exchange, the ocean absorbs roughly a third of Cant, meaning that Cant is an additional source of carbon for the ocean. In particular, the North Atlantic is known to be a region with a high storage capacity of Cant. Whereas the distribution of Cant in the upper layers of the North Atlantic is well documented, its transport to the abyssal ocean and the mechanisms behind its deep redistribution remain scarcely described. To shed light on this research gap, we use a database provided by ~70 Deep-Argo floats equipped with oxygen sensors and located in the North Atlantic that allow us to explore the deep pathways of Cant. First, the macronutrients and carbon variables (pH, total alkalinity, total inorganic carbon and pCO2) are estimated with bayesian neural networks (CANYON-B and CONTENT) from the temperature, salinity and oxygen data of the floats. Second, Cant concentrations in the water column are then estimated with back-calculation methods. Here we present the first results of our studyN

Identifying and addressing the anthropogenic drivers of global change in the North Sea: a systematic map protocol

BACKGROUND: Anthropogenic pressures on marine ecosystems have increased over the last 75 years and are expected to intensify in the future with potentially dramatic cascading consequences for human societies. It is therefore crucial to rebuild marine life-support systems and aim for future healthy ecosystems. Nowadays, there is a reasonable understanding of the impacts of human pressure on marine ecosystems; but no studies have drawn an integrative retrospective analysis of the marine research on the topic. A systematic consolidation of the literature is therefore needed to clearly describe the scientific knowledge clusters and gaps as well as to promote a new era of integrative marine science and management. We focus on the five direct anthropogenic drivers of biodiversity loss defined by the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES): (1) climate change; (2) direct exploitation; (3) pollution; (4) biological invasions; and (5) sea-use change. Our systematic map’s regional focus lies on the North Sea, which is among the most impacted marine ecosystems around the globe. The goal of the present study is to produce the first comprehensive overview of how marine research on anthropogenic drivers in the North Sea has grown and changed over the past 75 years. Ultimately, this systematic map will highlight the most urgent challenges facing the North Sea research domain. METHODS: The search will be restricted to peer-reviewed articles, reviews, meta-analyses, book chapters, book reviews, proceeding papers and grey literature using the most relevant search engines for literature published between 1945 and 2020. All authors will participate in the adjustment of the search in order to consider all relevant studies analyzing the effect of the direct anthropogenic drivers on the North Sea marine ecosystem. The references will be screened for relevance according to a predefined set of eligibility/ineligibility criteria by a pool of six trained reviewers. At stage one, each abstract and title will be independently screened by two reviewers. At stage two, potentially relevant references will be screened in full text by two independent reviewers. Subsequently, we will extract a suite of descriptive meta-data and basic information of the relevant references using the SysRev platform. The systematic map database composed will provide the foundation for an interactive geographical evidence map. Moreover, we will summarize our findings with cross-validation plots, heat maps, descriptive statistics, and a publicly available narrative synthesis. The aim of our visualization tools is to ensure that our findings are easily understandable by a broad audience