Community Research and Development Information Service - CORDIS

H2020

GCP-GEOTARCTIC Report Summary

Project ID: 657853
Funded under: H2020-EU.1.3.2.

Periodic Reporting for period 1 - GCP-GEOTARCTIC (Geochemical-physical coupled study of the modern Arctic Ocean: GEOTRACES-ARCTIC)

Reporting period: 2015-07-01 to 2017-06-30

Summary of the context and overall objectives of the project

At present, our ability to evaluate the full impact of climate-driven alterations of the Arctic Ocean (sea ice cover, hydrography, circulation) and predict their future trajectory is limited by a poor understanding of the interacting chemical, physical and biological processes that shape the functional characteristics and resiliency of Arctic waters. To bridge this critical knowledge gap, a pan-Arctic field study (Arctic-GEOTRACES, http://www.geotraces.org) has been coordinated between Canada, US, Germany and France to generate a quasi-synoptic database of biogeochemical tracers of circulation, ecosystem structure and productivity, and sea ice state. The Canadian program involves 28 investigators including biological, chemical and physical oceanographers, experimentalists and modellers.
Fully integrated in this program, the proposed research focuses on trace elements (Rare Earth Elements; REE) and isotopes (ɛNd, 230Th and 231Pa) that provide powerful tracers of ocean circulation and land/ocean chemical exchanges, both impacted by climate change in the Arctic. It was conducted on the Canadian section, itself connected to the US Arctic GEOTRACES section and the French GEOVIDE section by common cross-over intercalibration stations.
The proposed study consists of a three-step approach:
i) Initial modelling study of Arctic Ocean dynamics, including off-line Lagrangian analyses to refine the sampling strategy for the tracers mentioned above;
ii) Measurements of these tracers on the Canadian section to specifically investigate land-ocean exchanges and circulation in the Arctic Ocean;
iii) Integration of these data into a fine resolution model coupling circulation, sea ice dynamics and biogeochemical processes to refine our understanding of circulation and to quantify land-ocean margin chemical exchanges of bioactive or water mass fingerprinting chemical elements.
Besides enriching international databases, results from this program will provide predictions of Arctic Ocean responses to climate change and other human-related disturbances, and foundational information critical for sustainable development in the Arctic.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The first part of Dr Melanie Grenier's project was to prepare and participate to the GEOTRACES program of the Canadian Arctic cruise (July-August 2015). In this context, she first ran modeled Lagrangian analyses to refine the sampling location of a coastal station in Baffin Bay.
In parallel, Dr Grenier also organized and realized an acid cleaning of the sampling material to do the collection of the seawater samples and the on-board chemical extraction of the desired elements from seawater in appropriate conditions. Finally, she followed a radionuclide safety and methodology course and familiarized herself with the methodology of the 230Th and 231Pa analyses in seawater.

As soon as she went back from the cruise, Dr Grenier began to perform the remaining chemistry on the samples to separate and purify the dissolved fractions of Pa and Th from the REE. In parallel, she set up an acid purification system (Savillex DST-1000) in Dr Francois' clean lab (UBC, EOAS department, Vancouver, BC, Canada) to produce high purity acids (hydrochloric and nitric acids) at a lower cost.
She measured the 231Pa concentrations of the samples in May 2016 and the 230Th ones in July 2016 on the inductively coupled plasma mass spectrometer (Element2, Thermo Scientific) of the department, coupled to a desolvating nebulizer system (Aridus II, CETAC) to increase the sensitivity and improve the measurements, and optimized this measurement method. Dr Grenier had a validated dataset in fall 2016 and started the interpretation part. She presented her results for the first time at the GEOTRACES meeting that took place in Winnipeg (AB, Canada) during the ArcticNet annual scientific meeting, in early December 2016.

Afterwards, Dr Grenier compiled her data with those previously published and those acquired by Dr Francois but unpublished, after control and validation of the unpublished data. Meanwhile, Dr Grenier started the redaction of a first article, reviewing the evolution of dissolved 230Th and 231Pa in the Amerasian Basin over the last 4 decades, article that will be submitted soon to the peer-reviewed scientific journal Earth and Planetary Sciences Letter.

From fall 2015, Dr Grenier also began to participate to the GEOTRACES modelling weekly meetings, coordinated by Dr Susan Allen. Through these meetings, Dr Grenier actively contributed to Cindy Yu's Master Thesis, which aimed at exploring the ongoing changes in intermediate layers of the Arctic Ocean from a geo-tracer perspective by configuring for the first time a three-dimensional Arctic 230Th and 231Pa model. Dr Grenier was a member of Cindy Yu's supervisory committee. Cindy Yu defended her Master thesis in April 2017 and is currently writing an article on her Master results for which Dr Grenier will be co-author.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Dissolved 230Th and 231Pa concentrations acquired from the seawater samples collected during the 2015 Canadian Arctic cruise by Dr Grenier will bring new understandings about water mass formations, circulations and particle concentrations in the modern Arctic.
Data from the Canada Basin emphasize a particle scavenging enhancement due to sea-ice thinning and retreat, and a potential widening of the intermediate boundary circulation.
Dr Grenier's research will also provide the first 3 profiles of dissolved 230Th and 231 Pa concentrations ever acquired in Baffin Bay and will likely bring critical information about the origins and formation processes of the Baffin Bay deep/bottom waters.
Finally, the 2 profiles measured in the 2015 Labrador Sea will be compared to the 2 published profiles collected in 1993 and 1999 in the area to investigate the evolution of deep water convection intensity in the Labrador Sea, a key parameter of the Meridional Overturning Circulation. Modelling studies will be performed in Baffin Bay and the Labrador Sea to test/complement the hypotheses raised by the data.

Within the next year, Dr Grenier will also process and measure the dissolved concentrations of REEs and the isotopic composition of neodymium (Nd IC) of the 2015 Canadian Arctic samples. These data will help to constrain the circulation hypotheses raised by the 230Th and 231Pa profiles. They will also likely bring new key information about the circulation sources and pathways, as well as about the intensity of boundary exchange, especially in the shallow and complex area connecting the Arctic and the Atlantic Oceans: the Canadian Arctic Archipelago (CAA).

From this project will result more than a hundred of new data for each studied tracer, characterizing more than 10 water-column profiles, in an area where these tracers were poorly documented so far. Therefore, this valuable data set will significantly contribute to the global geochemical database enrichment, a crucial point to better understand the cycle of these elements in the ocean and the processes in which they are involved, and to control that we use them as tracers of appropriate oceanic processes, principles on which the international GEOTRACES program is based. Besides, the acquisition of new and numerous geochemical data and their understanding is of prime importance to properly develop and constrain coupled physical/geochemical oceanic models.

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