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Surface‐derived meltwater can access the bed of the Greenland ice sheet, causing seasonal velocity variations. The magnitude, timing, and net impact on annual average ice flow of these seasonal perturbations depend on the hydraulic efficiency of the subglacial drainage system. We examine the relationships between drainage system efficiency and ice velocity, at three contrasting tidewater glaciers in southwest Greenland during 2014–2019, using high‐resolution remotely sensed ice velocities, modeled surface melting, subglacial discharge at the terminus, and results from buoyant plume modeling. All glaciers underwent a seasonal speed‐up, which usually coincided with surface melt onset, and subsequent slow‐down, which usually followed inferred subglacial channelization. The amplitude and timing of these speed variations differed between glaciers, with the speed‐up being larger and more prolonged at our fastest study glacier. At all glaciers, however, the seasonal variations in ice flow are consistent with inferred changes in hydraulic efficiency of the subglacial drainage system and qualitatively indicative of a flow regime in which annually averaged ice velocity is relatively insensitive to interannual variations in meltwater supply—so‐called "ice flow self‐regulation." These findings suggest that subglacial channel formation may exert a strong control on seasonal ice flow variations, even at fast‐flowing tidewater glaciers. Plain Language Summary: Each summer, meltwater produced at the surface of the Greenland ice sheet reaches and lubricates its base, causing the overlying ice to accelerate. Continual water flow during the summer months melts hydraulically efficient drainage pathways (conduits) into the basal ice, enabling rapid evacuation of water and causing the overlying ice to decelerate. At fast‐flowing glaciers, like those studied here, basal conduit formation is thought to be disrupted, thereby negating its braking effect. We test this idea by examining ice flow and meltwater discharge at three ocean‐terminating glaciers, of varying velocities, over 5 years. Every year, each glacier initially accelerated in response to surface melting, then decelerated following inferred basal conduit formation. The acceleration was greater, and deceleration smaller, at glaciers that were faster flowing on average. At all our studied glaciers, however, we found that the formation of basal conduits caused ice flow deceleration. This suggests that, even at very fast glaciers, basal conduits can form and exert a strong control on glacier velocity at seasonal timescales. Key Points: We use high‐resolution ice velocity estimates and plume modeling and observations to investigate drivers of seasonal ice flow variabilityWe observe large seasonal ice flow variations; the amplitude, pattern, and longevity of which varied between glaciersSeasonal subglacial channel evolution can explain these flow variations, which result in minimal interannual differences in ice flow [ABSTRACT FROM AUTHOR]

Iceberg discharge is estimated to account for up to 50% of the freshwater flux delivered to glacial fjords. The amount, timing, and location of iceberg melting impacts fjord‐water circulation and heat budget, with implications for glacier dynamics, nutrient cycling, and fjord productivity. We use Sentinel‐2 imagery to examine seasonal variations in freshwater flux from open‐water icebergs in Sermilik Fjord, Greenland during summer and fall of 2017–2018. Using iceberg velocities derived from visual‐tracking and changes in total iceberg volume with distance down‐fjord from Helheim Glacier, we estimate maximum average two‐month full‐fjord iceberg‐derived freshwater fluxes of ~1,060 ± 615, 1,270 ± 735, 1,200 ± 700, 3,410 ± 1,975, and 1,150 ± 670 m3/s for May–June, June–July, July–August, August–September, and September–November, respectively. Fluxes decrease with distance down‐fjord, and on average, 86–91% of iceberg volume is lost before reaching the fjord mouth. This method provides a simple, invaluable tool for monitoring seasonal and interannual iceberg freshwater fluxes across a range of Greenlandic fjords. Plain Language Summary: Recent studies have shown that the freshwater produced via the melting of icebergs can dominate the freshwater budget in glacial fjords surrounding the Greenland Ice Sheet, which has important implications for fjord circulation and heat budget, nutrient availability, and primary productivity. Here we use satellite imagery to estimate both iceberg velocity and the seasonal changes in iceberg volume in Sermilik Fjord in southeast Greenland in 2017–2018, from which meltwater fluxes are derived. Iceberg meltwater fluxes are highest in the late summer and fall, when fjord water temperatures are warmer than in the spring and early summer, and when more icebergs have been calved into the fjord. Throughout the year, the volume of freshwater generated from the melting of icebergs is greater than the freshwater entering the fjord at the base of the glacier and sourced from melting at the ice sheet surface. As such, the melting of icebergs provides a significant volume of freshwater to the fjord system, with important implications for fjord‐scale circulation and heat budget, nutrient cycling, and primary productivity. The methodology presented here is effective, simple and inexpensive, and can be applied to a variety of glacial fjord systems, particularly those that are remote and inaccessible. Key Points: Freshwater fluxes from iceberg melt in Sermilik Fjord have a seasonal signal, peaking across August and September in 2017 and 2018Fluxes decrease with distance down‐fjord from Helheim Glacier, with ~86–91% of iceberg volume lost before reaching the fjord mouthWe present a simple and effective tool for monitoring iceberg freshwater fluxes across a range of Greenlandic fjords [ABSTRACT FROM AUTHOR]

Quantification of climate forcing of glacial hydrological systems at the decadal scale is rare because most measurement stations are too far downstream for glacier impacts to be clearly detected. Here we apply a measure of daily hydrograph entropy to a unique set of reliable, high‐altitude gauging stations, dating from the late 1960s. We find a progressive shift to a greater number of days with diurnal discharge variation as well as more pronounced diurnal discharge amplitude. These changes were associated with the onset of rapid warming in the 1980s as well as declining end of winter snow depths as inferred from climate data. In glaciated catchments, lower winter snow depths reduce the magnitude and duration of snowpack buffering and encourage the earlier onset of glacier ice exposure, with associated lower surface albedo and more rapid melt. Together, these processes explain the increase in the observed intensity of diurnal discharge fluctuations. Plain Language Summary: River basins that have a high proportion of ice cover are particularly sensitive to climate warming. Daily variations in insolation and temperature typically lead to fluctuations in snow and/or ice melt and thus a daily rise and fall in river flow. Snow, and the glaciers themselves, can buffer this rise and fall. For six high mountain Alpine basins, we show that daily discharge fluctuations are changing due to climate warming at the decadal scale, with both increasing daily discharge maxima and reducing daily discharge minima. These changes reflect decreased snow accumulation at the end of winter, reducing the buffering and increasing the onset of rapid glacier melt. Key Points: A Shannon Entropy Index is used to quantify changing daily hydrograph shape for six high‐altitude Alpine basins, with a range of degrees of glacier cover, between 1969 and 2014For the five most glaciated basins, there has been an increase in the frequency and amplitude of diurnal discharge fluctuations since the onset of more rapid warming in the 1980sThese changes in diurnal discharge are driven by reduced snow buffering of ice melt and runoff resulting from declining end of winter snow depths and greater mean annual temperatures [ABSTRACT FROM AUTHOR]

Uniform within-row plant spacing is a key crop management strategy to achieve high corn (Zea mays L.) yield. A new precision planting concept is emerging based on the use of modern devices in planters. The objective of this study was to investigate the impact of optimizing within-row plant spacing to enhance plant nutritional status and corn yield. The treatments investigated were (a) traditional planter with mechanical horizontal plate metering system (TP), (b) precision planter with vSet (Precision Planting, Tremont, IL) vacuum meter system (PP) and (c) PP pulled by a tractor equipped with an real time kinematic (RTK)-based auto-steering system (APP). The experimental design was a randomized block with three replications, and the plant evaluations were determined based on a main plot and a plant-to-plant study. Two types of vegetation indexes (VI and normalized diff erence, NDVI) were used for assessing plant nutritional status. A high standard of uniform plant spacing (CV < 10%) was required to achieve the highest corn yield. Optimizing the within-row plant spacing resulted in higher VI and NDVI. Based on the average of two experiments, PP improved the uniformity of plant spacing (CV = 22.5%) compared to TP (CV = 38.7%). This optimization of within-row plant spacing increased the corn yield by 10.7%. Only in the year with higher corn yield potential did APP result in a yield increase of 6.9% in relation to PP. Although the precision planters investigated had decreased the error in plant distribution, no one reached the plant spacing uniformity required to achieve higher corn yields. [ABSTRACT FROM AUTHOR]

Recent acceleration of Greenland's ocean‐terminating glaciers has substantially amplified the ice sheet's contribution to global sea level. Increased oceanic melting of these tidewater glaciers is widely cited as the likely trigger, and is thought to be highest within vigorous plumes driven by freshwater drainage from beneath glaciers. Yet melting of the larger part of calving fronts outside of plumes remains largely unstudied. Here we combine ocean observations collected within 100 m of a tidewater glacier with a numerical model to show that unlike previously assumed, plumes drive an energetic fjord‐wide circulation which enhances melting along the entire calving front. Compared to estimates of melting within plumes alone, this fjord‐wide circulation effectively doubles the glacier‐wide melt rate, and through shaping the calving front has a potential dynamic impact on calving. Our results suggest that melting driven by fjord‐scale circulation should be considered in process‐based projections of Greenland's sea level contribution. Plain Language Summary: As the world warms, loss of ice from the Greenland Ice Sheet will be a significant source of sea level rise. Greenland loses ice partly through the flow of huge rivers of ice called tidewater glaciers that dump solid ice directly into the ocean. Over the past two decades, tidewater glaciers around Greenland have accelerated dramatically, increasing Greenland's contribution to global mean sea level. There is mounting evidence that these accelerations have been driven by ocean warming, and a resulting increase in the rate at which the ocean melts the front of tidewater glaciers (called submarine melting). Yet submarine melting is at present poorly understood, in part due to the danger and difficulty of collecting data close to tidewater glaciers. We present observations of the ocean in front of a tidewater glacier that are unprecedented in their proximity to the glacier. These data reveal an ocean circulation which flushes warm water along the front of the glacier, driving high rates of submarine melting. We then use a numerical model to identify what drives this circulation. Our results are an important step toward understanding a key process which will modulate future sea level contribution from the Greenland ice sheet. Key Points: Ocean observations that are unprecedented in their spatial detail and proximity to a Greenlandic tidewater glacier are reportedDespite being highly localized, plumes drive fjord‐wide circulation and hence glacier‐wide submarine melting at tidewater glaciersFjord‐scale submarine melting drives significant mass loss and may promote calving, hence is a key process determining glacier stability [ABSTRACT FROM AUTHOR]