Impact of glacial activity on the weathering of Hf isotopes – Observations from Southwest Greenland

Rickli, Jörg; Hindshaw, Ruth S.; Leuthold, Julien; Wadham, Jemma L.; Burton, Kevin W.; Vance, Derek

doi:10.1016/j.gca.2017.08.005

Cited by 11 publications

(25 citation statements)

References 92 publications

(9 reference statements)

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“…The hydrology and chemistry of the Leverett River during the 2009 melt-season have previously been reported (Bartholomew et al, 2011;Hindshaw et al, 2014;Rickli et al, 2017) and the main results are summarized here. The hydrology was typical for a glacierized catchment with strong seasonal variation.…”

Section: Water Samplesmentioning

confidence: 91%

“…Previous work on water draining the Leverett Glacier, an outlet glacier in the Kangerlussuaq area (Figure 1), used Ca, Sr, Nd, and Hf data of water, rock, and mineral separates to constrain chemical weathering reactions contributing to the dissolved load (Hindshaw et al, 2014;Rickli et al, 2017). Our aim in this study was to analyse mineral separates, bulk rock samples, sediments, and water samples for δ 26 Mg and δ 7 Li in order to test whether the dissolution of silicate minerals previously identified as controlling the dissolved load composition in this catchment were consistent with dissolved δ 26 Mg and δ 7 Li values from this region or whether a carbonate contribution to dissolved δ 26 Mg is indeed required.…”

Section: Figure 1 | (A)mentioning

confidence: 99%

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Mg and Li Stable Isotope Ratios of Rocks, Minerals, and Water in an Outlet Glacier of the Greenland Ice Sheet

2019

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Magnesium and lithium stable isotope ratios (δ 26 Mg and δ 7 Li) have shown promise as tools to elucidate biogeochemical processes both at catchment scales and in deciphering global climate processes. Nevertheless, the controls on riverine Mg and Li isotope ratios are often difficult to determine as a myriad of factors can cause fractionation from bulk rock values such as secondary mineral formation and preferential weathering of isotopically distinct mineral phases. Quantifying the relative contribution from carbonate and silicate minerals to the dissolved load of glacierized catchments is particularly crucial for determining the role of chemical weathering in modulating the carbon cycle over glacial-interglacial periods. In this study we report Mg and Li isotope data for water, river sediment, rock, and mineral separates from the Leverett Glacier catchment, West Greenland. We assess whether the silicate mineral contributions to the dissolved load, previously determined using radiogenic Sr, Ca, Nd, and Hf isotopes, are consistent with dissolved Mg and Li isotope data, or whether a carbonate contribution is required as inferred previously for this region. For δ 7 Li, the average dissolved river water value (+19.2 ± 2.5 , 2SD) was higher than bedrock, river sediment, and mineral δ 7 Li values, implying a fractionation process. For δ 26 Mg, the average dissolved river water value (−0.30 ± 0.14 , 2SD) was within error of bedrock and river sediment and within the range of mineral δ 26 Mg values (−1.63 to +0.06). The river δ 26 Mg values are consistent with the mixing of Mg derived from the same mineral phases previously identified from radiogenic isotope measurements as controlling the dissolved load chemistry. Glacier fed rivers previously measured in this region had δ 26 Mg values ∼0.80 lower than those measured in the Leverett River which could be caused by a larger contribution from garnet (−1.63) dissolution compared to Leverett. This study highlights that dissolved Mg and Li isotope ratios in the Leverett River are affected by different processes (mixing and fractionation), and that since variations in silicate mineral δ 26 Mg values exist, preferential weathering of individual silicate minerals should be considered in addition to carbonate when interpreting dissolved δ 26 Mg values.

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Section: Water Samplesmentioning

confidence: 91%

Section: Figure 1 | (A)mentioning

confidence: 99%

Mg and Li Stable Isotope Ratios of Rocks, Minerals, and Water in an Outlet Glacier of the Greenland Ice Sheet

2019

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“…The role of hydrology and geology was recently demonstrated at a Canadian glacier where seasonal variations in εNd in a geologically heterogeneous catchment were attributed to the changes in subglacial hydrology (distributed to channelised) which altered where erosion occurred (Clinger et al, 2016). In contrast, glacial catchments with more homogenous lithology have little seasonal variation in εNd (Clinger et al, 2016;Rickli et al, 2017). From this small dataset (this study, Viers et al, 2008;Garçon et al, 2013;Clinger et al, 2016) it would appear that seasonal variations of εNd in suspended sediments are present where rivers drain mixed geology and have a pronounced seasonality to their hydrological cycle.…”

Section: Implications For Nd As a Sediment Source Tracermentioning

confidence: 99%

Clay mineralogy, strontium and neodymium isotope ratios in the sediments of two High Arctic catchments (Svalbard)

et al. 2018

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Abstract. The identification of sediment sources to the ocean is a prerequisite to using marine sediment cores to extract information on past climate and ocean circulation. Sr and Nd isotopes are classical tools with which to trace source provenance. Despite considerable interest in the Arctic Ocean, the circum-Arctic source regions are poorly characterised in terms of their Sr and Nd isotopic compositions. In this study we present Sr and Nd isotope data from the Paleogene Central Basin sediments of Svalbard, including the first published data of stream suspended sediments from Svalbard.The stream suspended sediments exhibit considerable isotopic variation (εNd = −20.6 to −13.4; 87 Sr / 86 Sr = 0.73421 to 0.74704) which can be related to the depositional history of the sedimentary formations from which they are derived. In combination with analysis of the clay mineralogy of catchment rocks and sediments, we suggest that the Central Basin sedimentary rocks were derived from two sources. One source is Proterozoic sediments derived from Greenlandic basement rocks which are rich in illite and have high 87 Sr / 86 Sr and low εNd values. The second source is Carboniferous to Jurassic sediments derived from Siberian basalts which are rich in smectite and have low 87 Sr / 86 Sr and high εNd values. Due to a change in depositional conditions throughout the Paleogene (from deep sea to continental) the relative proportions of these two sources vary in the Central Basin formations. The modern stream suspended sediment isotopic composition is then controlled by modern processes, in particular glaciation, which determines the present-day exposure of the formations and therefore the relative contribution of each formation to the stream suspended sediment load. This study demonstrates that the Nd isotopic composition of stream suspended sediments exhibits seasonal variation, which likely mirrors longer-term hydrological changes, with implications for source provenance studies based on fixed endmembers through time.

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“…Merschel et al [31] showed Incongruent Hf weathering and the decoupling of the Hf-Nd isotope systems due to the 'zircon effect' is less effective during glacial intervals. Either intense glacial mineral grinding and more congruent weathering [35] or longer water-rock interaction time during glacial intervals are suggested to be the responsible for less pronounced Hf-Nd isotope decoupling [36] in seawater. During non-glacial intervals, however, it was shown that trapping of unradiogenic Hf in zircons accounts for 70% up to 99% of the Hf-Nd decoupling on the continental hinterland to reproduce the seawater array by only weathering and erosion processes [22,27].…”

Section: Hf-nd Decoupling On the Continentsmentioning

confidence: 99%

“…Although some studies suggest that boundary exchange processes between sediment and seawater are plausible mechanisms to explain the radiogenic Hf isotopic composition of seawater [28,65], the sorption and dilution mechanisms behind these processes are not known. Rickli et al [36] postulated that the small offset between dissolved Hf-Nd river data and seawater may (similarly to Nd) be explained by boundary exchange processes.…”

Section: Benthic Flowsmentioning

confidence: 99%

Hf-Nd Isotopes in Archean Marine Chemical Sediments: Implications for the Geodynamical History of Early Earth and Its Impact on Earliest Marine Habitats

Viehmann

2018

Geosciences

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Abstract:The Hf-Nd isotope systems are coupled in magmatic systems, but incongruent Hf weathering ('zircon effect') of the continental crust leads to a decoupling of the Hf-Nd isotope systems in low-temperature environments during weathering and erosion processes. The Hf-Nd isotope record was recently dated back from the Cenozoic oceans until the Archean, showing that both isotope systems were already decoupled in seawater 2.7 Ga ago and potentially 3.4 Ga and 3.7 Ga ago. While there might have existed a hydrothermal pathway for Hf into Archean seawater, incongruent Hf weathering of more evolved, zircon-bearing uppermost continental crust that was emerged and available for subaerial weathering accounts for a significant decoupling of Hf-Nd isotopes in the dissolved (<0.2 µm) and suspended (>0.2 µm) fractions of Early Earth's seawater. These findings contradict the consensus that uppermost Archean continental crust was (ultra)mafic in composition and predominantly submerged. Hence, Hf-Nd isotopes in Archean marine chemical sediments provide the unique potential for future research to trace the emergence of evolved continental crust, which in turn has major implications for the geodynamical evolution of Early Earth and the nutrient flux into the earliest marine habitats on Earth.

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Impact of glacial activity on the weathering of Hf isotopes – Observations from Southwest Greenland

Abstract: General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. Full terms of use are available: http://www.bristol.ac.uk/pure/about/ebr-terms

Cited by 11 publications

References 92 publications

Mg and Li Stable Isotope Ratios of Rocks, Minerals, and Water in an Outlet Glacier of the Greenland Ice Sheet

Mg and Li Stable Isotope Ratios of Rocks, Minerals, and Water in an Outlet Glacier of the Greenland Ice Sheet

Clay mineralogy, strontium and neodymium isotope ratios in the sediments of two High Arctic catchments (Svalbard)

Hf-Nd Isotopes in Archean Marine Chemical Sediments: Implications for the Geodynamical History of Early Earth and Its Impact on Earliest Marine Habitats

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