DOI: 10.5884/13263
title: Study of Sea Ice Biogeochemistry (snow depth, ice thickness, ice salinity, dissolved inorganic carbon, total alkalinity, biomass, under ice currents) Comparing a Thick First Year Ice Site, and a Thinner Polynya Site Near Cambridge Bay

description: The selected sites were both on level first year ice: one approximately 5 km to the east of the Finlayson Islands, outside of the polynya where we expected weaker currents and thick first-year ice, and one directly between the islands, in the polynya where we expected strong currents and thin first-year ice. Sampling was conducted over a 6-day period between 4 and 10 May 2019, with both sites visited on three days (4, 7, and 10 May).  On the first sampling date, inverted tilt current meters (Lowell Instruments TCM-1 Current Meter) were installed at both sites to measure velocity (units: cm s-1) in 1-minute intervals. Sea ice sampling was conducted at the sites using a Kovacs Mark II 9-cm diameter coring system. Snow depth (units: cm) was measured with a meter stick prior to collection; ice thickness (units: cm) was measured after core collection with a measuring tape. One core was collected at each site on each day for temperature and salinity profiles. Temperature (units: degrees C) was measured using a Thermopen Mk4 temperature probe at 10-cm intervals. The core was cut into 10-cm sections, which were sealed in plastic bags, melted, and analyzed for salinity using a YSI multiparameter probe (units: PSU). For sea ice carbonate sampling, 10-cm sections were cut and sealed in the field. Samples were melted in the lab, and transferred to 160-mL borosilicate bottles using a peristaltic pump and fixed with mercuric chloride. At each site, we obtained one “high-resolution” core for TIC and TA (10 May), where sections were collected every 10 cm from top to bottom. On each date, 5 locations were randomly selected within a 10-m radius of the centre point of each site. At each of these locations a core was extracted to collect the top, bottom, and middle 10 cm for TIC and TA analysis. This yielded a total of 15 samples for each horizon (top, middle, bottom) for each site. Ice samples from the bottom 5 cm of three additional cores were combined in an opaque jug, melted in the lab, and filtered for Chl a analysis. Laboratory analysis was conducted at the University of Calgary and the University of Manitoba. TIC was determined through acid extraction (units: umol kg-1) ,TA was measured by modified Gran Titration (units: umol kg-1). Remaining sample water was then analyzed for salinity (units: PSU) using conductivity meter. Chl a concentration was determined by fluorometry and converted to biomass (units: mg m-2) by multiplying by the length of the core section.
description: This study is about the carbonate chemistry of sea ice. Sea ice carbonate chemistry is thought to play an important role in global carbon cycles (i.e the uptake and storage of carbon dioxide from the atmosphere) but exactly how important is subject to considerable debate. One of the reasons for this uncertainty is that there is considerable variability in the reported total alkalinity (TA) to total inorganic carbon (TIC) ratio between different studies. Usually, this disparity is explained by spatial variability - different sea ice sites experience different physical, biological, and chemical characteristics, leading to large variations in the TA:TIC ratio of sea ice. To study variability in sea ice TA and TIC, we selected a site about 30 km west of Cambridge Bay (Iqaluktuttiaq), Nunavut. The site is a known location of an "invisible polynya", a location where strong under-ice currents lead to thinner ice and potentially higher ice algae biomass. We used two sites - one outside of the polynya, and one within the polynya - to perform a statistical comparison of TIC and TA. Our hypothesis was that due to the strong variations in physical (currents, ice thickness) and biological (ice algae) conditions, we would observe significant spatial variability in sea ice carbonate chemistry.