Award: OPP-1753408

This grant allowed us to participate in the international Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) during 2019-2020. The overall goal of the MOSAiC expedition was to study the Arctic Ocean and atmosphere for an entire year, including over the Arctic winter, taking the closest look ever at the Arctic, as the epicenter of global warming, and to gain fundamental insights to better understand global climate change. The goals of this particular project were to collect and analyze aerosol particles in the Arctic atmosphere, investigate their sources and solubility, and measure the rate of transfer of material from the atmosphere to sea ice and the open ocean. Atmospheric transport and deposition of aerosols is an important delivery mechanism of natural and contaminant trace elements to the oceans, including the Arctic Ocean. Inputs of contaminant elements such as lead and mercury, and of biologically essential elements such as manganese, iron, cobalt, and zinc have strong impacts on the ecosystem. The assessment of these inputs to the remote central Arctic Ocean has been difficult, particularly during the winter months because of the limited opportunities to make aerosol chemistry and deposition measurements on a routine basis. We were able to collect samples to assess aerosol trace element fluxes and partitioning among the various catchments (seawater, sea ice and snow) in the central Arctic Ocean from October 2019 to May 2020. We collected and analyzed 26 aerosol filter samples (on a roughly weekly sampling schedule) for Be-7 and trace element analysis. These samples include bulk aerosols as well as aerosol samples separated into coarse and fine particle sizes. Because direct measurements of wet and dry aerosol deposition are difficult and unreliable, we utilized Beryllium-7 (Be-7) as a tracer for analyzing trace element atmospheric fluxes and catchment partitioning. Be-7 is a naturally occurring radioactive element that is created in the atmosphere by cosmic rays and deposited on the ocean surface primarily through precipitation. The Be-7 method is a well-established means of determining aerosol fluxes to the ocean surface and involves the measurement of the isotope inventory in seawater, ice, and snow, as well the Be-7 concentrations in aerosol particles. Catchment inventories were calculated using 25 large volume (1000L) seawater samples from the upper ocean, 20 ice core samples, and over 100 snow samples. As a result of our Be-7 analysis, as well as snow depth and ice thickness measurements, we were able to measure seasonal changes in fluxes and partitioning of trace elements among the seawater/ice/snow reservoirs. For example, we found that Be-7 seawater inventories decreased after freeze-up according to the Be-7 decay rate. This strongly suggests that the upper water column remains isolated from atmospheric input beginning in late September, and that new aerosol deposition is partitioned exclusively into the snow cover until the spring melt season commences. Low precipitation rates and snow depths (~10cm on level sea ice) were observed during the winter months, and our Be-7 data suggest that aerosol deposition rates reached a minimum in late winter and early spring. Overall, aerosol trace element concentrations in the Arctic were low, at levels of nanograms per cubic meter of filtered air. Lithogenic elements like iron, aluminum, titanium, and thorium remained consistently low in the winter-time samples from the central Arctic. These elements did not increase in concentration until the ship began to travel southward toward the North Atlantic in May 2020. In contrast, elements produced by anthropogenic activities including copper, zinc, nickel, and chromium were relatively higher during the winter months (December-March) than during the spring (April-May). This latter group of elements was also enriched compared to typical values in crustal material. When this material is deposited to the surface ocean, either directly or after interception by sea ice, the constituent elements will impact marine biogeochemical cycles. The magnitude of this impact is a function how much of each trace element dissolves from the aerosol particles. To measure the fractional solubility and potential bioavailability of each element we use chemicals that are meant to approximate important natural processes. For example, we expose the aerosol particles to ultrapure water to mimic their uptake into rain droplets. We use dilute acids to mimic the harsher environment aerosol particles would experience in the gut of a zooplankton or fish. These data will be available to other researchers and will inform our collective understanding of biogeochemical cycles in the Arctic. This project supported the professional development of three early-career scientists at the Skidaway Institute of Oceanography. Two graduate students received extensive training in analytical techniques using samples from the MOSAiC project. They have applied that training to projects of their own with one having completed their Masters degree and the other working toward a PhD. A postdoctoral researcher participated in Leg 3 of the MOSAiC expedition and has been leading the analytical work. Last Modified: 04/02/2024 Submitted by: WilliamMLanding