Polar inland waters, encompassing Arctic and Antarctic regions, are experiencing unprecedented environmental changes. Warming air temperatures and shifting precipitation patterns are leading to shortened ice durations, novel flow regimes, and altered ecosystem dynamics, affecting the biodiversity and functioning of polar lakes and rivers. This session aims to bring together scientists from diverse disciplines to share their research findings, discuss key issues, and identify future directions for understanding the implications of long-term changes on ecosystem dynamics and hydrological processes in polar environments. Through this multidisciplinary session, we aim to foster collaboration and facilitate the exchange of knowledge among researchers working on various aspects of polar limnology to better understand global change.
Lead Organizer: Hilary Dugan, University of Wisconsin–Madison (hdugan@wisc.edu)
Co-organizers:
Arial Shogren, University of Alabama (ashogren@ua.edu)
Václava (Vendy) Hazuková, University of Maine (vaclava.hazukova@maine.edu)
Presentations
04:00 PM
Thermal Structure and Oxygen Depletion in Ice-covered Lakes (8285)
Primary Presenter: Sally MacIntyre, University of California - Santa Barbara (sally@eri.ucsb.edu)
Arctic lakes are ice-covered for 9 months or more of the year yet mean temperatures and thermal structure and oxygen dynamics can vary considerably within one lake and between lakes of different morphometries. Here we use time series data obtained year round for over ~15 years for temperature and at least 4 years for specific conductance and oxygen to assess controls on variability in 5 lakes on the North Slope of Alaska ranging in size from 1 to 150 ha. Mean temperatures in winter primarily depended on mean summer temperatures in the lakes a few ha in size whereas heat loss in fall was a larger control on the lakes greater than 10 ha. Patterns of fall cooling determined the dates of ice on, with the smaller lakes freezing two to ten days earlier than the larger lake. When ice on followed winds of 5 m s-1, initial thermal stratification was less than 1oC. When stratification was greater, internal waves persisted for a few days. Mean winter temperatures were independent of initial stratification. Oxygen depletion varied with lake morphometry with higher loss rates in smaller lakes with their larger ratio of sediment area to volume. The transfer of heat and solutes was moderated by gravity currents, penetrative convection induced when light penetrated through the ice which also contributed to heating, and internal wave motions. Antecedent conditions and within lake hydrodynamics shaped the thermal and density structure which in turn influences biogeochemistry and organism habitat.
04:15 PM
What is the role of hydrological connectivity in shaping carbon dioxide concentrations and emissions in Arctic lakes? (8227)
Primary Presenter: Vaclava Hazukova, University of Maine (vaclava.hazukova@maine.edu)
The role of Arctic lakes as sites of carbon processing is amplified with rapidly changing climate leading to permafrost thaw and altered hydrological connections. Land-to-water hydrological connections represent an important regulatory mechanism of carbon transport, especially in systems with low rainfall-runoff ratios such as the Arctic tundra. While the importance of hydrological connectivity has been inferred locally, there is no assessment of its role at a pan-Arctic scale across different lake types. To better understand how hydrological connectivity controls annual aquatic carbon dioxide concentrations and emissions, we collated previously published and unpublished data from more than 200 Arctic lakes distributed across permafrost regions in Alaska, Northern Canada, Greenland, Siberia, and Scandinavia. To characterize land-to-lake connections, we delineated lake catchments and characterized climate, land topography, soil properties, and land use within each watershed. High hydrological connectivity is associated with relatively low carbon dioxide concentrations, low emissions, and low across-lake variability. Regions with low hydrological connectivity characterized by low effective precipitation have very high across-lake variability of both concentrations and fluxes, having both the lowest and the highest measured concentrations and fluxes. Lakes with the highest emissions (top 25%) are in low-relief lowlands in the zone of continuous/discontinuous permafrost and have smaller catchments with a high proportion of wetlands.
04:30 PM
Thermal Overturning Circulation in an Arctic Pond (7840)
Primary Presenter: Stephen Henderson, Washington State University (steve_henderson@wsu.edu)
In a 1.5-m-deep arctic pond (68.626N,149.597W), bottom-water renewal observed during early summer was dominated by thermal overturning circulation, rather than by wind-driven overturning or vertical turbulent mixing. Water velocities and rates of viscous dissipation of turbulent energy were estimated using three pulse-coherent Nortek Aquadopp ADCPs, while temperature stratification was measured along three vertical profiles using 41 RBR Solo-T temperature loggers. Mixing displayed strong daily cycles, with a warm, <0.5-m-deep surface mixed layer during daytime, which cooled and thickened to ~0.75 m during night-time free convection. At greater depths, daily cycles of cooling and warming were also observed (+/-2°C), but strong stratification separated upper and lower layers. During both day and night, this stratification prevented significant vertical turbulent mixing between the surface mixed layer and underlying waters. Each night, in a layer extending 10 cm above the gently sloping bed near the pond’s inlet, temperatures were colder than those in underlying sediments, or those near the pond’s deepest point. We infer that these relatively cold waters were created by surface cooling in very shallow regions of the pond or the adjacent wetland, and cascaded down the bed to renew bottom waters. A bottom-water heat balance suggests about 40 m3 of bottom water renewal each night, sufficient to replace most bottom water despite the absence of deep-pond turbulent mixing. The observed thermal overturning circulation likely influences heat transport and biogeochemical cycling.
04:45 PM
Estimation of under-ice light by Bayesian modelling using a global dataset (7961)
Primary Presenter: Gaia Donini, University of Trento (gaia.donini@unitn.it)
Ice-covered lakes are isolated from the atmosphere, and light penetrating the ice is one of the main mechanisms to warm lake water during wintertime. Accurate quantification of under-ice light is therefore crucial for assessing biological activity and physical dynamics during the ice-covered season. At present, direct measurements of under-ice light are limited, mainly due to logistical difficulties during the winter season. Therefore, in practice, the fraction of light penetrating through the ice cover is estimated by an exponential decay described by the Beer-Lambert law through the ice, knowing the albedo, the thickness and composition of the ice cover (black ice, white ice and snow), and the light extinction coefficient of each layer. However, literature values for the light extinction coefficient are generally site-specific and rare, which poses limitations. In this work, we collected a dataset of light measurements both above and below ice, and total ice and snow thickness from 46 lakes in the Northern Hemisphere with 828 daily measurements (including 15 lakes and 628 measurements with ice quality information). Based on the Beer-Lambert law, we developed a Bayesian model for predicting under-ice light and incorporating a comprehensive uncertainty assessment, given the thickness of each layer and the above-ice light. The use of a large data set allows a stable estimation of the distribution of light extinction coefficients. Coupled with ice thickness models, it can be used to provide insights into future trends in light availability in lakes worldwide.
05:00 PM
Consequences of a Changing Cryosphere for Arctic Lake Biogeochemistry (7740)
Primary Presenter: Ansley Grider, University of Maine (ansley.grider@maine.edu)
The fate of heavy metals and nutrients melting out of the cryosphere into aquatic systems is not well understood. To address this, we measured heavy metals and nutrients in the water and sediment of four glacially fed (GF) and four snow and groundwater-fed (SF) lakes in West Greenland during the summer of 2023. GF lakes had significantly higher (133%) water concentrations of nutrients (TP, NO3-, NH4+) and metals (Cd, Pb, Cr, Co, Ni, Al, Fe, Cu, Zn) compared to nearby SF lakes. This pattern was reflected in the sediments, where metal concentrations were generally higher in GF lakes compared to SF lakes. However, a few metals, notably Hg and Pb, were higher in SF compared to GF sediment. In all lakes, metals have generally increased over time. In one GF lake, we quantified inputs and outputs of metals and nutrients, and found that loads declined by an average of 69% from the lake inlet to outlet, suggesting the lake was a sink for these materials. Our results highlight that GF lakes in our study region are elevated in nutrients and metals compared to nearby SF lakes, indicating that the source of these materials is likely glacial meltwater. These results also show that GF lakes have the ability to sequester a high percent of the nutrients and metals flowing into the lakes; however, as meltwater fluxes increase due to climate change, the ability of these lakes to remain sinks is an open question.
05:15 PM
Compound climate extremes in a shoulder season altered hydrologic connectivity and abruptly transformed Arctic lakes of West Greenland (8037)
Primary Presenter: Jasmine Saros, University of Maine (jasmine.saros@maine.edu)
We investigated the response of lakes in West Greenland to compound climate extremes (both record heat and rainfall) associated with a series of atmospheric rivers in autumn 2022. West Greenland lakes are among the 25% of total circumpolar lake area situated in arid, low relief regions. We compared early and late summer 2023 responses to those collected in all previous years (2013-2019 early summer, 2021 and 2022 late summer). Lakewater isotopes were depleted, indicating reduced evaporation in autumn 2022; the altered hydrology substantially increased terrestrial-aquatic linkages. Throughout summer 2023, lake color was more than 220% higher than all previous years, leading to a coherent transition from “blue” to “brown” lakes in less than a year, with water clarity reduced by 50%, owing to changes in DOM quality and increased iron concentrations. Implications for planktonic communities will also be discussed. The abrupt transformation of these lakes highlights how the timing of compound extreme events determines the strength of effects.
SS29A - Limnology of Polar Environments
Description
Time: 4:00 PM
Date: 4/6/2024
Room: Meeting Room KL