Understanding the links between pelagic microbial ecosystems and organic matter cycling in the changing Arctic

The Arctic Ocean's key role in regulating the global climate is highly sensitive to climate change. Arctic temperatures have increased more strongly than the global average during the recent past, causing a loss of multiyear sea-ice and fundamental changes in ecosystem structure and function. Arctic primary production and biogeochemical cycling are projected to change. Longer ice-free periods and thinner sea-ice increase light availability, enhancing phytoplankton production, which may also be further stimulated by increased carbon dioxide.

We have assembled a multidisciplinary UK/German team to address this NERC/BMBF Arctic call with a renowned track record of pioneering research concerning the structure and function of marine pelagic ecosystems, including extensive research in the Arctic. This project has the overarching aim to improve our understanding of how short-term (e.g. seasonal- scale) and long-term (e.g. climate-driven) changes in the physical environment of the Arctic Ocean are impacting pelagic microbial ecosystems and how these affect current and future organic matter (OM) biogeochemistry.

The focus of our activities principally addresses Challenge 1 "To develop quantified understanding of the structure and functioning of Arctic ecosystems". Our multidisciplinary team with expertise in marine microbial ecology, OM biogeochemistry, polar plankton ecology, and ecosystem modelling will fully characterise the microbial base (archaea, bacteria, protists including phytoplankton and fungi) of the pelagic Arctic food web in relation to OM cycling. Through a comprehensive multi-location and multi-seasonal cruise programme we will address major knowledge gaps in the links between Arctic microbial ecosystem structure and function across a broad range of sea-ice environments. Our sampling strategy, including the rarely sampled winter and early spring, will allow us to quantify impacts of Arctic seasonality on the structure and functioning of microbial ecosystems in relation to OM cycling, allowing us to track major changes in autotrophic and heterotrophic production. Combining observation and modelling, we will analyse the underlying mechanisms that impact microbial dynamics and subsequent OM cycling on seasonal scales. The model setup will integrate forcing data and results of NEMO-MEDUSA simulations. Data-model synthesis will enable us to resolve and constrain processes that remain either unresolved or are assumed constant in MEDUSA. Our model results will thus specify uncertainty ranges that may be accounted for in future projections of the Arctic with NEMO-MEDUSA and the UK Earth System Model (UKESM).

We have assembled a multidisciplinary UK/German team to address the NERC/BMBF Arctic. The team has a renowned track record of pioneering research concerning the structure and function of pelagic marine ecosystems, including extensive research in the Arctic. The overarching aim of the project is to improve our understanding of how short-term (e.g. seasonal) and long-term (e.g. climate-driven) changes in the physical environment of the Arctic Ocean are impacting pelagic microbial ecosystems and how these affect current and future OM biogeochemistry. The work packages link to additional collaborators and existing NERC Arctic Consortia to maximise research impact, value and links to stakeholders (e.g. NEMO-MEDUSA).

Marine Systems Modelling Group/NEMO-MEDUSA
A primary stakeholder and major user of our research is the Marine Systems Modelling (MSM) Group at the National Oceanography Centre (NOC). We have fully engaged with the Marine Systems Modelling Group at the NOC during the proposal planning stages, and they have provided enthusiastic support for our project. The proposed work in WP4 and WP5 will develop and evaluate important processes that are not currently resolved within the NEMO-MEDUSA ocean modelling environment. As a result of our study, there will be long-term improvements in the performance of NEMO- MEDUSA and the UKESM within the Arctic environment. Our Interaction with NEMO-MEDUSA will be collaborative, because they have agreed to provide forcing data and results from simulations for 1998 to 2015 that will be used for model development in WP4.

Atmospheric and Global Carbon Cycle Research Community
Atmospheric scientists have become more aware of the importance of pelagic biological processes in Arctic marine ecosystems. We will also collaborate with two world-leading research groups, with expertise in atmospheric chemistry (TROPOS) and the functioning of the biological carbon pump (SEAPUMP). A specific aim of these collaborations is to ensure that our research has impact beyond our own specific research fields. Through working with our collaborators, we can produce direct links between our study of structure and function of pelagic marine ecosystems and both the Arctic atmosphere and the broad-scale functioning of the biological carbon pump.

Societal Impact
The general public have a broad interest in marine life and environmental issues, including the diversity of marine organisms and climate change. They are fascinated with life in polar ecosystems, with large charismatic mammals (e.g. polar bears, seals) often their main focus. The Marine Biological Association is a learned society formed in 1884 and incorporated by royal charter in 2013, with an international membership (1,500 in 46 countries) that includes marine science professionals, students and the public. Our work will show the amazing diversity and abundance of microbial components of Arctic ecosystems, and the roles that they have in large-scale ecological and biogeochemical processes. Our observations linking marine microbes with ecosystem functioning in the Arctic will be of interest to all members of the association.