Arctic freshwater biodiversity is rapidly changing due to climate warming, resource extraction, infrastructure development, and landscape transformation. To improve understanding, predict future responses, and inform policy formulation, research needs must be clearly identified. Using a horizon scan survey, Arctic freshwater experts from government, international agencies, and Indigenous Peoples identified 77 biodiversity rese...

Factors leading to exceptionally high temperatures in shallow tropical waters are examined with high‐resolution measurements and application of a 3‐dimensional hydrodynamic model in an Amazon floodplain lake. Highest near‐surface (0.05 m) temperatures in open water ranged from 31.0 to 37.5°C. Within mats of floating plants maximum temperatures ranged from 33.7 to 39.8°C, and within flooded forests from 30.6 to 34.1°C. Highest...

Recent experimental and modeling work predicted salt fingers, known in saline water bodies, would form under ice in freshwater lakes with specific conductance (SC) as low as 50 μ S cm −1 . To test this prediction, Toolik Lake, Alaska (summer SC 60–90 μ S cm −1 ) was instrumented with temperature‐conductivity arrays. Calculations of solutes excluded with ice formation and a mass balance of changes in concentration of solutes wi...

Ice‐covered lakes differ strongly from their ice‐free counterparts in their temperatures, heat budgets, and hydrodynamics. Nevertheless, due to a lack of detailed measurements, processes under the ice and their drivers are still understudied. Here we present a multiyear study of five arctic lakes ranging from 1 to 150 ha focusing on temperature and thermal stratification during ~ 200 d of ice cover. Mean water temperatures dur...

The CO 2 flux () from lakes to the atmosphere is a large component of the global carbon cycle and depends on the air–water CO 2 concentration gradient (ΔCO 2 ) and the gas transfer velocity ( k ). Both ΔCO 2 and k can vary on multiple timescales and understanding their contributions to is important for explaining variability in fluxes and developing optimal sampling designs. We measured and ΔCO 2 and derived k for one full ice...

Processes regulating the rate of oxygen depletion determine whether hypoxia occurs and the extent to which greenhouse gases accumulate in seasonally ice‐covered lakes. Here, we investigate the oxygen budget of four arctic lakes using high‐frequency data during two winters in three shallow lakes (9–13 m maximal depth) and four winters in 24 m deep main basin of Toolik Lake. Incubation experiments measured sediment metabolism. V...

The hydrodynamics within small boreal lakes have rarely been studied, yet knowing whether turbulence at the air–water interface and in the water column scales with metrics developed elsewhere is essential for computing metabolism and fluxes of climate‐forcing trace gases. We instrumented a humic, 4.7 ha, boreal lake with two meteorological stations, three thermistor arrays, an infrared (IR) camera to quantify surface divergenc...

Small ice‐covered lakes are stratified by temperature and solutes. Using time series measurements and profiles of temperature, specific conductance (SC), and dissolved oxygen obtained during spring 2014 and 2015, we identified the physical processes occurring under the ice and at ice‐off in two ~ 2 ha, 10‐m‐deep arctic lakes. The lakes are distinguished from other freshwater, ice‐covered lakes by solutes initially stabilizing...

Small ponds, numerous throughout the Arctic, are often supersaturated with climate‐forcing trace gases. Improving estimates of emissions requires quantifying (1) their mixing dynamics and (2) near‐surface turbulence which would enable emissions. To this end, we instrumented an arctic pond (510 m 2 , 1 m deep) with a meteorological station, a thermistor array, and a vertically oriented acoustic Doppler velocimeter. We contraste...

The extent to which snowmelt flowing into ice‐covered lakes spreads horizontally and mixes vertically influences retention of solutes derived from the landscape. To quantify these transport processes and retention, we combine time series temperature and specific conductance measurements in Toolik Lake (Alaska) and its major inflow, with measurements of discharge and meteorology, and profiles of specific conductance, temperatur...

Winter conditions are rapidly changing in temperate ecosystems, particularly for those that experience periods of snow and ice cover. Relatively little is known of winter ecology in these systems, due to a historical research focus on summer ‘growing seasons’. We executed the first global quantitative synthesis on under‐ice lake ecology, including 36 abiotic and biotic variables from 42 research groups and 101 lakes, examining...

Permafrost thaw lakes occur in high abundance across the subarctic landscape but little is known about their limnological dynamics. This study was undertaken to evaluate the hourly, seasonal, and depth variations in oxygen concentration in three thaw lakes in northern Quebec, Canada, across contrasting permafrost regimes (isolated, sporadic, and discontinuous). All lakes were well stratified in summer despite their shallow dep...

We characterize stratification patterns over diel, seasonal, and annual time scales in inshore and offshore regions of Lake Victoria, East Africa; determine conditions leading to horizontal exchanges; and, using surface energy budgets derived from local meteorological stations and two reanalysis products, address whether stratification depends on advective as opposed to local processes. The largest change in the surface energy...

To quantify the effect of basin morphometry on internal wave dynamics, we installed thermistor arrays around the perimeter of Mono Lake, California. The lake's complex bathymetry includes alongshore bottom slopes ranging from

A series of vertical profiles of dissolved oxygen (DO) collected periodically over two consecutive ice‐free seasons in an oligotrophic high‐elevation lake (Emerald Lake, California) were used to investigate volumetric and areal rates of gross primary production (GPP), community respiration (CR), and net ecosystem production (NEP). Diel patterns in DO did not weaken with depth in this lake, where the entire 10‐m water column wa...

Arctic climate change is leading to accelerated melting of permafrost and the mobilization of soil organic carbon pools that have accumulated over thousands of years. Photochemical and microbial transformation will liberate a fraction of this carbon to the atmosphere in the form of CO 2 and CH 4 . We quantified these fluxes in a series of permafrost thaw ponds in the Canadian Subarctic and Arctic and further investigated how o...

Mean epilimnetic temperatures from mid‐June through mid‐August in a small, arctic kettle lake had no trend from 1975 to 2008 and varied annually up to ±3°C relative to the mean. Analysis of data from temperature arrays deployed on the lake from 1998 to 2007 showed that as mean summer temperatures shifted from 2.5°C below the mean, to the mean, and to 3°C above the mean, deepening of the mixed layer during cold fronts decreased...

We describe the flow paths of negatively buoyant river inflows in a small lake with multiple basins separated by sills (Toolik Lake, Alaska) using field data and three‐dimensional simulations. Comparisons of field observations, analytical computations, and simulations show that in small basins in which the timescale for filling (τ f ) is less than the timescale of an event (τ 0 ), overflow is the dominant mechanism of interbas...

Describing the spatial and temporal occurrence of turbulent mixing and the mechanisms of turbulence production are fundamental problems in physical limnology and oceanography. Here we present results from Mono Lake, California, that illustrate pronounced steepening of the pycnocline upon cessation of strong wind forcing and the enhanced turbulence resulting from this nonlinearity. Three events occurred with wind speed of >10 m...

To determine the relative importance of different sources of nitrate to the annual nitrogen needs of the giant kelp Macrocystis pyrifera , we measured ambient nitrate concentrations at a kelp forest for 13 months and characterized nitrate delivery using water column thermal structure and flow data collected in the forest and at its offshore edge. The forest's monthly nitrate supply varied by a factor of 50, while measured net...