Micro-ARC

Description

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 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 Research Challenge 1 of the CAO programme: “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).

Objectives

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 organic matter (OM) biogeochemistry.

The project is based around five integrated work packages (WP). The WPs are also linked with activities of complementary collaborators, NEMO-MEDUSA, the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition and the existing NERC Arctic Consortia.

WP1 Microbial community structure and function

How do pelagic microbial abundance, activity and diversity change seasonally, and in relationship to microgels?

WP2 Plankton changes in size/biomass distributions

How do seasonal changes in size distributions of phytoplankton and other protists in open-ocean and ice-covered areas affect carbon transfer functions?

WP3 Organic matter quality and quantity

How does OM quality and quantity, including microgels, change seasonally, and in relationship to changes in microbial community structure and productivity?

WP4 Model development and data-model synthesis

What are the underlying mechanisms that let the size structure of Arctic microbial communities differ from those of lower latitude oceans, and how could these differences possibly be incorporated into simple models with global scope?

WP5 Modelling organic matter fluxes

How do seasonal qualitative changes in POM and DOM affect annual flux estimates of carbon and nitrogen? How sensitive are heterotrophic processes under continuous dark winter conditions to changes in photo-autotrophic OM production and gel formation under continuous light conditions?