Seasonal evolution of water contributions to discharge from a Greenland outlet glacier: insight from a new isotope-mixing model

Bhatia, Maya P.; Das, Sarah B.; Kujawinski, Elizabeth B.; Henderson, Paul B.; Burke, Andrea; Charette, Matthew A.

doi:10.3189/002214311798043861

Cited by 51 publications

(70 citation statements)

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“…Hence, by its nature, distributed system meltwater should acquire significantly higher 222 Rn activities than meltwater that flows through open channels. Discrete 222 Rn measurements in small glacial watersheds have been used to infer the transition from distributed to channelized drainage (Kies et al, 2011;Bhatia et al, 2011;Kies et al, 2015). This paper expands upon these earlier studies by examining the utility of long term continuous 222 Rn measurements in the proglacial river of a large GrIS outlet glacier during the spring and summer of 2011 and 2012.…”

Section: Introductionmentioning

confidence: 91%

Utility of 222Rn as a passive tracer of subglacial distributed system drainage

Linhoff

Charette

Nienow

et al. 2017

Earth and Planetary Science Letters

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Keywords: radon Greenland glacier proglacial river meltwater Water flow beneath the Greenland Ice Sheet (GrIS) has been shown to include slow-inefficient (distributed) and fast-efficient (channelized) drainage systems, in response to meltwater delivery to the bed via both moulins and surface lake drainage. This partitioning between channelized and distributed drainage systems is difficult to quantify yet it plays an important role in bulk meltwater chemistry and glacial velocity, and thus subglacial erosion. Radon-222, which is continuously produced via the decay of 226 Ra, accumulates in meltwater that has interacted with rock and sediment. Hence, elevated concentrations of 222 Rn should be indicative of meltwater that has flowed through a distributed drainage system network. In the spring and summer of 2011 and 2012, we made hourly 222 Rn measurements in the proglacial river of a large outlet glacier of the GrIS (Leverett Glacier, SW Greenland). Radon-222 activities were highest in the early melt season (10-15 dpm L −1 ), decreasing by a factor of 2-5 (3-5 dpm L −1 ) following the onset of widespread surface melt. Using a 222 Rn mass balance model, we estimate that, on average, greater than 90% of the river 222 Rn was sourced from distributed system meltwater. The distributed system 222 Rn flux varied on diurnal, weekly, and seasonal time scales with highest fluxes generally occurring on the falling limb of the hydrograph and during expansion of the channelized drainage system. Using laboratory based estimates of distributed system 222 Rn, the distributed system water flux generally ranged between 1-5% of the total proglacial river discharge for both seasons. This study provides a promising new method for hydrograph separation in glacial watersheds and for estimating the timing and magnitude of distributed system fluxes expelled at ice sheet margins. Published by Elsevier B.V.

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Section: Introductionmentioning

confidence: 91%

Utility of 222Rn as a passive tracer of subglacial distributed system drainage

Linhoff

Charette

Nienow

et al. 2017

Earth and Planetary Science Letters

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“…Stable isotopes provide evidence for assessing plant water sources according to their variations caused by equilibrium and kinetic isotopic fractionation mechanisms (Orlowski et al, 2016a;Haverd et al, 2011;Zhao et al, 2013;Bhatia et al, 2011). Several studies (Liu et al, 2013;Mathieu and Bariac, 1996;Allison and Barnes, 1985) have shown that transpiration do not cause isotopic fractionation of soil water.…”

Section: Introductionmentioning

confidence: 99%

Soil water migration in the unsaturated zone of semiarid region in China from isotope evidence

Yang

2017

Hydrol. Earth Syst. Sci.

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Abstract. Soil water is an important driving force of the ecosystems, especially in the semiarid hill and gully region of the northwestern Loess Plateau in China. The mechanism of soil water migration in the reconstruction and restoration of Loess Plateau is a key scientific problem that must be solved. Isotopic tracers can provide valuable information associated with complex hydrological problems, difficult to obtain using other methods. In this study, the oxygen and hydrogen isotopes are used as tracers to investigate the migration processes of soil water in the unsaturated zone in an arid region of China's Loess Plateau. Samples of precipitation, soil water, plant xylems and plant roots are collected and analysed. The conservative elements deuterium (D) and oxygen ( 18 O) are used as tracers to identify variable source and mixing processes. The mixing model is used to quantify the contribution of each end member and calculate mixing amounts. The results show that the isotopic composition of precipitation in the Anjiagou River basin is affected by isotopic fractionation due to evaporation. The isotopic compositions of soil waters are plotted between or near the local meteoric water lines, indicating that soil waters are recharged by precipitation. The soil water migration is dominated by piston-type flow in the study area and rarely preferential flow. Water migration exhibited a transformation pathway from precipitation to soil water to plant water. δ 18 O and δD are enriched in the shallow (< 20 cm depth) soil water in most soil profiles due to evaporation. The isotopic composition of xylem water is close to that of soil water at the depth of 40-60 cm. These values reflect soil water signatures associated with Caragana korshinskii Kom. uptake at the depth of 40-60 cm. Soil water from the surface soil layer (20-40 cm) comprised 6-12 % of plant xylem water, while soil water at the depth of 40-60 cm is the largest component of plant xylem water (ranging from 60 to 66 %), soil water below 60 cm depth comprised 8-14 % of plant xylem water and only 5-8 % is derived directly from precipitation. This study investigates the migration process of soil water, identifies the source of plant water and finally provides a scientific basis for identification of model structures and parameters. It can provide a scientific basis for ecological water demand, ecological restoration, and management of water resources.

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“…The majority of meltwater discharged from the Greenland ice sheet first drains contact (Bhatia et al, 2011). In the present study, discharge was also measured at the were substantially higher than a filter process blank (see below) such that we were able to 111 utilize these samples for Fe analyses.…”

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confidence: 67%

“…For example, at Haut 554 Glacier d'Arolla, a similarly-sized Swiss Alps glacier with a schist-gneiss-amphibolite 555 bedrock, sulfate concentrations in the bulk runoff are typically less than 200 µeq/L, but 556 borehole waters sampled at the bed could have a sulfate concentrations up to 1200 µeq/L 557 (Tranter et al, 2002). An exception to dilute sulfate concentrations in the 'N' glacier 558 runoff was the May 21 st sample which drained the lowest measured discharge waters with 559 the largest modeled delayed (basal) flow component (Bhatia et al, 2011). The sulfate 560 concentration in this sample was 929 µeq/L, thus hinting that some component of the 'N' 561 subglacial hydrological system may drain regions that support microbially-mediated 562 anoxic sulfide oxidation.…”

Section: Introduction 1mentioning

confidence: 98%

“…glacier, whose physical characteristics, local meteorology, and hydrology have been 95 described in detail elsewhere (Bhatia et al, 2011). In brief, we proposed that the 96 subglacial drainage at 'N' glacier seasonally evolves from a distributed to channelized 97 flow system, in which the 'Early May' runoff drains a delayed flow dominated, 98 hydraulically inefficient network and the 'Late May' and 'July' runoff drains an 99 increasingly glacial ice-melt dominated, hydraulically efficient network [Bhatia et al, The Early May waters were comprised of > 49% contribution from delayed flow waters, 104 whereas the Late May and July waters had between 12-36% and 5-17% respective 105 contributions from delayed flow (Bhatia et al, 2011 2-and silicate) analyses were collected in 500-mL high-density polyethylene 124 (HDPE) wide-mouth bottles (Nalgene). All samples were filtered on-site immediately 125 through 0.22 µm cellulose acetate membranes (GE) with a polypropylene vacuum 126 filtration apparatus (Nalgene).…”

Section: Introduction 1mentioning

confidence: 99%

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Hydrological and biogeochemical cycling along the Greenland ice sheet margin

Bhatia¹

2012

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Global warming has led to a significant increase in Greenland ice sheet (GrIS) melt and runoff since 1990, resulting in escalated export of fresh water and associated sediment to the surrounding North Atlantic and Arctic Oceans. Similar to alpine glacial systems, surface meltwater on ice sheet surface drains to the base (subglacial) where it joins a drainage system and can become chemically enriched from its origin as dilute snow-and ice-melt. In this thesis, I examine the interdependence of glacial hydrology and biogeochemical cycling in terms of export of carbon and iron from the Greenland ice sheet. I develop a new isotope mixing-model to quantify water source contributions to the bulk meltwater discharge draining a GrIS outlet glacier. Results illustrate (a) the new application of a naturally occurring radioisotope (radon-222) as a quantitative tracer for waters stored at the glacier bed, and (b) the seasonal evolution of the subglacial drainage network from a delayed-flow to a quick-flow system. Model results also provide the necessary hydrological context to interpret and quantify glacially-derived organic carbon and iron fluxes. I combine bulk-and molecular-level studies of subglacial organic carbon to show that GrIS discharge exports old (radiocarbon depleted), labile organic matter. Similar investigations of dissolved and particulate iron reveal that GrIS discharge may be a significant flux of labile iron to the North Atlantic Ocean during the summer meltseason. Both carbon and iron are subject to proglacial processing prior to export to the marine environment, and exhibit strong seasonal variability in correlation with the subglacial drainage evolution. Low, chemically concentrated fluxes characterize the spring discharge, whereas higher, chemically dilute fluxes typify the summer discharge. Collectively, this thesis provides some of the first descriptions and flux estimates of carbon and iron, key elements in ocean biogeochemical cycles, in GrIS meltwater runoff. 3 AcknowledgmentsThis thesis represents over half a decade of work for which there is a village of people to thank. First and foremost, my co-advisors, Elizabeth Kujawinski and Sarah Das: I feel so fortunate to have had the chance to work with such amazing scientists. I indebted to them for taking me on when we only had unfunded ideas, for tirelessly writing grants until we were funded, for always encouraging scientific discourse, and for their unfailing support, empathy, and encouragement. I feel that the mark of a great advisor is one who ultimately cares as much, if not more, for the student's development as for the research, and I am thankful to have had this in Sarah and Liz. They will be role models and friends throughout my scientific career. Matt Charette was in many ways a third advisor to me -a deal I'm not sure he bargained for! He graciously (and patiently) offered me his time, expertise, and free reign in his lab. My thesis is much richer as a result of his heavy involvement. I am also grateful to my committee members, Be...

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Seasonal evolution of water contributions to discharge from a Greenland outlet glacier: insight from a new isotope-mixing model

Cited by 51 publications

References 56 publications

Utility of 222Rn as a passive tracer of subglacial distributed system drainage

Utility of 222Rn as a passive tracer of subglacial distributed system drainage

Soil water migration in the unsaturated zone of semiarid region in China from isotope evidence

Hydrological and biogeochemical cycling along the Greenland ice sheet margin

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