Transport and transformation of riverine neodymium isotope and rare earth element signatures in high latitude estuaries: A case study from the Laptev Sea

Laukert, Georgi; Bauch, Dorothea; Hathorne, Ed C; Gutjahr, Marcus; Janout, Markus; Hölemann, Jens

doi:10.1016/j.epsl.2017.08.010

Cited by 29 publications

(60 citation statements)

References 52 publications

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“…In fact, the near-bottom salinity record on the northwestern shelf (not shown) shows a shifting increase by 0.5 just before 2013, which could be related to the seasonal sea ice changes there (Figure 11). FIGURE 12 | Total river water fraction (in %) (color-coded dots) and contributions (in %) of individual rivers (numbers: first and second number quantify Lena and Ob/Yenisey contributions, respectively) based on a water mass assessment previously reported by Laukert et al (2017) for the late summers of 2013 (left) and 2014 (right).…”

Section: Seasonal Cycles and Regional Contrasts In Stratificationmentioning

confidence: 99%

On the Variability of Stratification in the Freshwater-Influenced Laptev Sea Region

et al. 2020

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In this paper, we investigate the seasonal and spatial variability of stratification on the Siberian shelves with a case study from the Laptev Sea based on shipboard hydrographic measurements, year-round oceanographic mooring records from 2013 to 2014 and chemical tracer-based water mass analyses. In summer 2013, weak onshore-directed winds caused spreading of riverine waters throughout much of the eastern and central shelf. In contrast, strong southerly winds in summer 2014 diverted much of the freshwater to the northeast, which resulted in 50% less river water and significantly weaker stratification on the central shelf compared with the previous year. Our year-long records additionally emphasize the regional differences in water column structure and stratification, where the northwest location was well-mixed for 6 months and the central and northeast locations remained stratified into spring due to the lower initial surface salinities of the river-influenced water. A 26 year record of ocean reanalysis highlights the region’s interannual variability of stratification and its dependence on winds and sea ice. Prior the mid-2000s, river runoff to the perennially ice-covered central Laptev Sea shelf experienced little surface forcing and river water was maintained on the shelf. The transition toward less summer sea ice after the mid-2000s increased the ROFI’s (region of freshwater influence) exposure to summer winds. This greatly enhanced the variability in mixed layer depth, resulting in several years with well-mixed water columns as opposed to the often year-round shallow mixed layers before. The extent of the Lena River plume is critical for the region since it modulates nutrient fluxes and primary production, and further controls intermediate heat storage induced by lateral density gradients, which has implications for autumnal freeze-up and the eastern Arctic sea ice volume.MAIN POINTS1.CTD surveys and moorings highlight the regional and temporal variations in water column stratification on the Laptev Sea shelf.2.Summer winds increasingly control the extent of the region of freshwater influence under decreasing sea ice.3.Further reductions in sea ice increases surface warming, heat storage, and the interannual variability in mixed layer depth.

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Section: Seasonal Cycles and Regional Contrasts In Stratificationmentioning

confidence: 99%

On the Variability of Stratification in the Freshwater-Influenced Laptev Sea Region

et al. 2020

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“…This raises the question of whether the increase in 228 Ra is accompanied by a similar increase in these other terrigenous constituents. In contrast to 228 Ra, where shelf inputs are predominant and we defined a virtual freshwater end‐member, DOM and other terrigenous components like REE (Laukert et al, ) have primarily freshwater sources. The correlation between 228 Ra and such river borne terrigenous components (not shown) is therefore in part fortuitous because the sources of these terrigenous inputs do not coincide.…”

Section: Discussionmentioning

confidence: 99%

Radium Isotopes Across the Arctic Ocean Show Time Scales of Water Mass Ventilation and Increasing Shelf Inputs

et al. 2018

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The first full transarctic section of 228 Ra in surface waters measured during GEOTRACES cruises PS94 and HLY1502 (2015) shows a consistent distribution with maximum activities in the transpolar drift. Activities in the central Arctic have increased from 2007 through 2011 to 2015. The increased 228 Ra input is attributed to stronger wave action on shelves resulting from a longer ice-free season. A concomitant decrease in the 228 Th/ 228 Ra ratio likely results from more rapid transit of surface waters depleted in 228 Th by scavenging over the shelf. The 228 Ra activities observed in intermediate waters (<1,500 m) in the Amundsen Basin are explained by ventilation with shelf water on a time scale of about 15-18 years, in good agreement with estimates based on SF 6 and 129 I/ 236 U. The 228 Th excess below the mixed layer up to 1,500 m depth can complement 234 Th and 210 Po as tracers of export production, after correction for the inherent excess resulting from the similarity of 228 Ra and 228 Th decay times. We show with a Th/Ra profile model that the 228 Th/ 228 Ra ratio below 1,500 m is inappropriate for this purpose because it is a delicate balance between horizontal supply of 228 Ra and vertical flux of particulate 228 Th. The accumulation of 226 Ra in the deep Makarov Basin is not associated with an accumulation of Ba and can therefore be attributed to supply from decay of 230 Th in the bottom sediment. We estimate a ventilation time of 480 years for the deep Makarov-Canada Basin, in good agreement with previous estimates using other tracers. RUTGERS VAN DER LOEFF ET AL. 4853

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“…(A) Compares the MR estuary to estuarine systems reviewed in Rousseau et al (2015). (B) Compares the MR estuary's "conservative mixing" with station 182-1 in Osborne et al (2015) to river/estuarine systems of the Laptev Sea (Figure 8a in Laukert et al, 2017), and the Amazon River estuary (Rousseau et al, 2015). Ce becomes amplified during salt induced coagulation of colloids in the estuary, which is responsible for the increase in the negative Ce anomaly with increasing salinity (Elderfield et al, 1990;Sholkovitz, 1995;Shiller, 2002).…”

Section: Controls On Ree In the Mississippi River Estuarymentioning

confidence: 99%

Rare Earth Elements Geochemistry and Nd Isotopes in the Mississippi River and Gulf of Mexico Mixing Zone

et al. 2018

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Rare earth elements (REE) concentrations were measured in surface waters collected across the salinity gradient in the Mississippi River estuary (i. e., Mississippi River plume, MRP), which includes the near-shore portion of the Louisiana Shelf. In addition, the neodymium (Nd) isotope compositions of two river water samples, and the acid leachable fractions of the associated suspended particulate matter (SPM), were quantified to compare Mississippi River water, and SPM with Gulf of Mexico waters. Despite the spatial limitations associated with sampling due to the size of the Mississippi River system, this study provides some important insights into the REE geochemistry of the MRP. The Mississippi River and its estuarine waters are enriched in the heavy REE (HREE) compared to the light REE (LREE) when normalized to shale composites. All water samples from the estuary also exhibit substantial negative Ce anomalies. In contrast to the majority of other estuaries investigated, removal of REE in the low salinity reaches of the Mississippi River estuary is less substantial. For example, approximately 50% of the river borne Nd is removed in the low salinity region (S < 10) of the Mississippi River estuary, compared to the estimated global average of ca. 70% removal of Nd for estuaries worldwide. We propose that the relatively low REE removal in the Mississippi estuary reflects the high pH (∼8) of the Mississippi River, where REE complexation with carbonate ions and natural organic ligands act to stabilize REE in solution. The Nd isotope composition of Mississippi River water near its outflow to the Gulf of Mexico is ε Nd(0) = −10.5. The acid leachable fraction of the associated SPM is more radiogenic (−9.95 ≤ ε Nd(0) ≤ −9.77), and closer to the generally more radiogenic Gulf of Mexico [ε Nd(0) = −9.0]. Sequential extraction of the Mississippi River bank sediment reveals substantially different Sm/Nd ratios for the operationally defined fractions of the sediment, which suggests variations in Nd isotope compositions between the labile fractions and the bulk sediment.

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Transport and transformation of riverine neodymium isotope and rare earth element signatures in high latitude estuaries: A case study from the Laptev Sea

Cited by 29 publications

References 52 publications

On the Variability of Stratification in the Freshwater-Influenced Laptev Sea Region

On the Variability of Stratification in the Freshwater-Influenced Laptev Sea Region

Radium Isotopes Across the Arctic Ocean Show Time Scales of Water Mass Ventilation and Increasing Shelf Inputs

Rare Earth Elements Geochemistry and Nd Isotopes in the Mississippi River and Gulf of Mexico Mixing Zone

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