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Tracing carbon exchanges/fluxes between Arctic and Atlantic basins

Periodic Reporting for period 1 - CarbEx (Tracing carbon exchanges/fluxes between Arctic and Atlantic basins)

Reporting period: 2019-11-01 to 2021-10-31

The Arctic Ocean (AO) is of great importance for climate regulation and carbon sequestration, contributing 5–14% to the global balance of CO2 sinks and sources. It is surrounded by land, with limited exchanges with its adjacent basins, the Atlantic (through the Fram Strait and Canadian Arctic Archipelago) and Pacific (through the Bering Strait) Oceans and great part of the Arctic outflow is exported through the Fram Strait. It is a unique ocean basin compared to the others, given the high loads of freshwater and dissolved organic matter (DOM) supplied by the Arctic Rivers. DOM is a large active Arctic organic carbon reservoir representing more than 95% of the organic carbon in the water and encompasses a wide range of compounds with variable molecular complexity, whose relative contribution varies in different environments, depending on its origin.
The Arctic environment is experiencing the brunt of global warming with the largest regional increases in atmospheric temperature (two- or three-fold the global average rate). This implies drastic reductions in summer sea-ice extent and enhanced glacier and ice sheet melt and permafrost thaw. This, in turn, leads to changes in freshwater export, production of DOM in river catchments and riverine transport of organic material into the Arctic seas. Studies on DOM in the region are needed for establishing current conditions and documenting coming changes propagating from river basins to the Arctic Ocean. However, given their difficult access, it is imperative to develop equipment and techniques for autonomously monitoring DOM in the remote Arctic Seas to accurately determine the fate and impact of mobilized carbon.
CarbEx employs spectroscopy measurements (e.g. absorption and fluorescence) and chemometrical data analysis combined to numerical modeling to assess and characterize the export of freshwater and dissolved organic matter (in terms of dissolved organic carbon–DOC) from the Arctic to the Atlantic Ocean through the Fram Strait.
The major findings (so far) of the project are that we can use FDOM to distinguish freshwater originated from the Eurasian and Canadian basins. We have also developed two methods within the project: one algorithm to estimate DOC concentrations from CDOM spectral properties and one method to estimate Arctic DOC export from moored platforms in the East Greenland Current. Project participants have also taken part in two reports with recommendations for Arctic research and sustainability in the context of the UN Ocean Decade for Sustainable Development and the European Polar Science Week. The project has also focused on communication, and we have submitted a manuscript for publication in Frontiers for Young Minds, where we aim to attract students to the field of marine sciences.
The project started in November 2019 and the accomplishments for the project (as of October 2021) with regards to the projects tasks (T), deliverables (D) and reached milestones (M) for each work package (WP) are given below (following the numbering presented in the proposal’s Gantt chart):

- WP1 – Data Assimilation and Processing
Compilation and analyses of in situ data set
Download, processing and validation of satellite remote sensing data
Perform PARAFAC analysis and water fractionation
Publish dataset in a public repository

- WP2 – Numerical modelling
Acquisition and compilation of data from Arctic rivers and moorings
Estimation of freshwater and DOC fluxes
Obtained estimates of freshwater and DOC fluxes

- WP3 –Ocean Color Remote Sensing and Temporal Variability
Generation of time series based on integrated satellite and numerical modelling results
Perform statistical analysis to assess temporal variability

- WP4 – Training, Communication, Dissemination, Exploitation and Public Engagement
Elaboration of Career Development Plan and Data Management Plan
Attendance of courses at DTU
Lecturing at DTU
Writing and submission of manuscripts to peer-reviewed journals
Presentation of findings at international conferences
Public engagement activities
Presentation of Career Development Plan to the section head at DTU
Presentation of Data Management Plan
The LEARN-TEACH Pilot Project (proposed as T4.9) was unfortunately not possible to be carried out due to the restrictions of the Covid-19 pandemic.

Changes in the program and schedule
- Tasks related to WP1 and WP2 were rescheduled to fit with the work developed during the secondment at the Norwegian Polar Institute (NPI). During the stay at NPI, we realized that we could use only mooring data to estimate the Arctic dissolved organic carbon (DOC) fluxes, as we developed a robust methodology that does not require earth system modelling applications as expected. Therefore, the modelling component of the project was replaced by the calculations performed based on the monthly timeseries obtained with ocean moorings.
- There were a few courses to attend in Spring (e.g. leadership and management, science communication) that were cancelled due to the Covid-19 pandemic.
CarbEx has estimated for the first time the monthly transport of Arctic DOC over a period of a decade. In this study two novel approaches are developed: an algorithm to estimate the DOC concentrations based on the optical properties of CDOM, and a methodology that allows to estimate the DOC export with the East Greenland Current in Fram Strait from volume transports estimated with ocean moorings.

I have contributed as co-author to an article (Stedmon et al 2021 JGR) where we have used in situ DOM data obtained with DOM fluorometers coupled to ice tethered profilers deployed in the Arctic Ocean. We showed the application of such data to trace the origins of Arctic surface waters, which was one of the objectives of CarbEx. I am leading another manuscript with focus on the Fram Strait only that is being prepared for submission.

The project has developed novel methodologies that will facilitate and have great impact on estimates of concentrations and fluxes of dissolved organic carbon, which is an important component of the aquatic carbon cycle, generally overlooked in biogeochemical models. The latter can be rectified with the upcoming publication of the Arctic biogeochemical database, which will provide basin-wide information on dissolved organic matter concentrations and composition with large potential to improve DOM parametrizations in biogeochemical models.

I joined the Arctic Ocean Decade Workshop in January 2020, during the Arctic Frontiers Conference in Tromsø. A report was published with inputs and recommendations to feed into the planning of the UN Ocean Decade for Sustainable Development. In October 2020, together with a colleague from DTU, I have chaired a discussion session in the European Polar Science Week. In the session with have discussed the implications and challenges that the predicted strong stratification at the Arctic Ocean’s surface will imply to the satellite remote sensing monitoring. We have established recommendations on how to tackle those limitations and how to move forward into a multi-platform synergistic biogeochemical monitoring of the changing Arctic Ocean. Those integrate the final report that was published in 2021. Those two reports are related to M4.5 (Present Policy strategy document). Those reports highlight the societal impacts of CarbEx given that those were forwarded to stakeholders and can be used for Arctic Policy.
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