The Arctic promise Loukacheva, Natalia
The Arctic promise,
c2007, 20070630, 2007, 2007-01-01, 2007-06-30
eBook
The Arctic Promisedeals with areas of comparative constitutional law, international law, Aboriginal law, legal anthropology, political science, and international relations, using each to contribute ...to the understanding of the right to indigenous autonomy.
The particle density (ρs) is a fundamental physical property needed for calculating the soil porosity and phase distributions. While ρs is often estimated using soil organic matter (SOM) content and ...particle size distribution, the specific densities of each soil component remain unclear in a subarctic agricultural setting. This study aimed to evaluate the ρs of soils from Southwest Greenland using a three‐compartment model (3CM) based on the mixing ratio of SOM derived from loss‐on‐ignition, mineral particles <20 μm (FC), and mineral particles ≥20 μm (CC). We further evaluated the accuracy of the 3CM against pedotransfer functions (PTFs) and visible near‐infrared (vis–NIR) spectroscopic models. A total of 324 soil samples from 16 Greenlandic agricultural fields were investigated, covering a wide range in SOM content (0.021–0.602 kg kg–1) and clay content (0.020–0.185 kg kg–1). Despite their high SOM content, the Greenlandic soils exhibited relatively high ρs (1.936–3.044 Mg m–3), which together with a large SOM/organic carbon ratio of 2.16 indicated a high SOM density of 1.493 Mg m–3. The 3CM fit on all soils indicated FC and CC densities of 3.047 and 2.713 Mg m–3, respectively, while a subset of soils (n = 203) from the same geological setting resulted in FC and CC densities of 2.738 and 2.731 Mg m–3. Prediction accuracy of the 3CM (RMSE = 0.067 Mg m–3) was similar to PTFs (RMSE = 0.068–0.070 Mg m–3) and better than vis–NIR spectroscopic models (RMSE = 0.091 Mg m–3).
Core Ideas
The particle density of South Greenlandic soils ranged from 1.94 to 3.04 Mg m−3.
Soil organic matter and soil fines content (<20 μm) were primary drivers of particle density.
A three‐compartment model was developed for particle density from soil organic matter, fines content, and soils particles >20 μm.
The three‐compartment model accuracy was similar (RMSE = 0.068 Mg m−3) to pedotransfer functions and better than spectroscopic models.
Organic C content‐based compartment models require careful consideration of the soil organic matter/organic C content ratio.
Southern West Greenland contains some of the best-studied and best-preserved magmatic Eoarchean rocks on Earth, and these provide an excellent vantage point from which to view long-standing questions ...regarding the growth of the earliest continental crust. In order to address the questions surrounding early crustal growth and complementary mantle depletion, we present Laser Ablation Split Stream (LASS) analyses of the U–Pb and Hf isotope compositions of zircon from eleven samples of the least-altered meta-igneous rocks from the Itsaq (Amîtsoq) Gneisses of the Isukasia and Nuuk regions of southern West Greenland. This analytical technique allows a less ambiguous approach to determining the age and Hf isotope composition of complicated zircon. Results corroborate previous findings that Eoarchean zircon from the Itsaq Gneiss (∼3.85 Ga to ∼3.63 Ga) were derived from a broadly chondritic source. In contrast to the Sm–Nd whole rock isotope record for southern West Greenland, the zircon Lu–Hf isotope record provides no evidence for early mantle depletion, nor does it suggest the presence of crust older than ∼3.85 Ga in Greenland.
Utilizing LASS U–Pb and Hf data from the Greenland zircons studied here, we demonstrate the importance of focusing on the magmatic (rather than detrital) zircon record to more confidently understand early crustal growth and mantle depletion. We compare the Greenland Hf isotope data with other Eoarchean magmatic complexes such as the Acasta Gneiss Complex, Nuvvuagittuq greenstone belt, and the gneissic complexes of southern Africa, and all lack zircons with suprachondritic Hf isotope compositions. In total, these data suggest only a very modest volume of crust was produced during (or survived from) the Hadean and earliest Eoarchean. There remains no record of planet-scale early Earth mantle depletion in the Hf isotope record prior to 3.8 Ga.
•LASS U–Pb and Hf isotope data are presented from eleven Eoarchean gneisses from Greenland.•Combined with previous studies, we conclude these gneisses were derived from a chondritic source.•There is no Hf isotope evidence for a widespread depleted mantle in the Eoarchean.•We emphasize the importance of the magmatic record for studying early Earth crustal growth.
Fast retreat of Zachariæ Isstrøm, northeast Greenland Mouginot, J.; Rignot, E.; Scheuchl, B. ...
Science (American Association for the Advancement of Science),
12/2015, Letnik:
350, Številka:
6266
Journal Article
Recenzirano
Odprti dostop
After 8 years of decay of its ice shelf, Zachariæ Isstrøm, a major glacier of northeast Greenland that holds a 0.5-meter sea-level rise equivalent, entered a phase of accelerated retreat in fall ...2012. The acceleration rate of its ice velocity tripled, melting of its residual ice shelf and thinning of its grounded portion doubled, and calving is now occurring at its grounding line. Warmer air and ocean temperatures have caused the glacier to detach from a stabilizing sill and retreat rapidly along a downward-sloping, marine-based bed. Its equal-ice-volume neighbor, Nioghalvfjerdsfjorden, is also melting rapidly but retreating slowly along an upward-sloping bed. The destabilization of this marine-based sector will increase sea-level rise from the Greenland Ice Sheet for decades to come.
Proglacial streams deliver melt water and chemical weathering products, including nutrients and radiogenic isotopes, from continental ice sheets to the ocean. Weathering products are also delivered ...to the ocean in non-glacial streams that form following ice sheet retreat and are disconnected from ice sheet meltwater by hydrologic divides. If weathering reactions differ in non-glacial and proglacial stream catchments, the streams could deliver different types and magnitudes of solutes to the ocean, depending on relative discharge volumes. Unlike proglacial streams, however, little is known of non-glacial stream solute compositions or discharge. Here we show specific discharges are similar from a proglacial stream draining the Greenland Ice Sheet (GrIS) with several streams disconnected from the ice sheet. We also evaluate weathering reactions across a 170-km transect in western Greenland that contains one proglacial stream draining the GrIS, and two coastal (ice distal) and three inland (ice proximal) areas with non-glacial streams. Non-glacial streams exhibit solute compositions and offsets between dissolved and bedload Sr isotope ratios that indicate weathering increases toward the coast with exposure age and precipitation. Major element mass balance calculations show weathering reactions shift from predominately carbonic acid weathering of carbonate minerals inland near the ice sheet to predominately sulfuric acid weathering of carbonate minerals near the coast. Strontium concentrations and isotopic ratios of the proglacial stream reflect mixing of at least two subglacial sources and minor in-stream weathering that consumes CO2. About 5 times less CO2 is consumed per liter in the proglacial than inland non-glacial streams; however, arid conditions inland suggest limited discharge from the ungauged inland streams leads to less total CO2 weathering than proglacial stream. One coastal area consumes less CO2 per liter than the proglacial stream and another coastal area exhibits net CO2 production. These results indicate estimates for glacial foreland solute fluxes and CO2 weathering consumption and production should include estimates from both non-glacial and proglacial streams. Understanding weathering fluxes from these two types of streams will be important for evaluations of past ice sheet retreat and predictions of future solute and CO2 fluxes associated with continued ice sheet retreat.
Marine-terminating outlet glaciers are a major source of modern ice loss from the Greenland Ice Sheet (GrIS), but their role in GrIS retreat during the last deglaciation is not well constrained. ...Here, we develop deglacial outlet glacier retreat chronologies for four regions in southwest and south Greenland to improve understanding of spatial variations in centennial- to millennial-scale ice loss under a warming climate. We calculate 10Be surface exposure ages of boulders located in fjords near the towns of Qaqortoq, Paamiut, Nuuk, and Sisimiut. Our northernmost study site, Sisimiut, deglaciated earliest at ∼18 ka to ∼15 ka with an average thinning rate of 0.1–0.3 m yr−1. Inland retreat from Sisimiut to the modern ice margin took ∼7 ka at an average retreat rate of 15–20 m yr−1. A 10Be-dated moraine ∼25 km from the modern GrIS margin deposited at ∼8 ka suggests a possible ice-margin still-stand, but this does not change overall retreat rates. After retreat from the small coastal Sisimiut fjords, the GrIS margin was mainly land-terminating in this region. In contrast, earliest exposure occurred at ∼12 ka near Qaqortoq, and 11–10 ka near Nuuk and Paamiut, with ice thinning at rates of 0.2–0.3 m yr−1 to instantaneous within measurement uncertainty. Ice retreat inland through the extensive Nuuk, Paamiut, and Qaqortoq fjord systems to near modern ice margins occurred in <1 ka, resulting in minimum retreat rates of 25–65 m yr−1 and maximum retreat rates of ∼95 m yr−1 to instantaneous within the uncertainty of our measurements. This rapid thinning and retreat of marine-terminating southwest GrIS margins is contemporaneous with an incursion of relatively warm ocean waters into the Labrador Sea and toward the southwest Greenland coast, suggesting that a warming ocean may have contributed to the more rapid retreat of marine GrIS termini in the Nuuk, Paamiut, and Qaqortoq fjord systems relative to the slower ice retreat inland from Sisimiut. Our results highlight past outlet glacier–ocean interaction as a potentially important driver in rapid GrIS retreat.
•SW Greenland marine ice-margins rapidly deglaciated 12–11 ka.•SW Greenland land ice-margins deglaciated slowly 18–7 ka.•Results suggest ocean environment drove rapid ice-margin retreat.
Glaciers distinct from the Greenland and Antarctic ice sheets are shrinking rapidly, altering regional hydrology
, raising global sea level
and elevating natural hazards
. Yet, owing to the scarcity ...of constrained mass loss observations, glacier evolution during the satellite era is known only partially, as a geographic and temporal patchwork
. Here we reveal the accelerated, albeit contrasting, patterns of glacier mass loss during the early twenty-first century. Using largely untapped satellite archives, we chart surface elevation changes at a high spatiotemporal resolution over all of Earth's glaciers. We extensively validate our estimates against independent, high-precision measurements and present a globally complete and consistent estimate of glacier mass change. We show that during 2000-2019, glaciers lost a mass of 267 ± 16 gigatonnes per year, equivalent to 21 ± 3 per cent of the observed sea-level rise
. We identify a mass loss acceleration of 48 ± 16 gigatonnes per year per decade, explaining 6 to 19 per cent of the observed acceleration of sea-level rise. Particularly, thinning rates of glaciers outside ice sheet peripheries doubled over the past two decades. Glaciers currently lose more mass, and at similar or larger acceleration rates, than the Greenland or Antarctic ice sheets taken separately
. By uncovering the patterns of mass change in many regions, we find contrasting glacier fluctuations that agree with the decadal variability in precipitation and temperature. These include a North Atlantic anomaly of decelerated mass loss, a strongly accelerated loss from northwestern American glaciers, and the apparent end of the Karakoram anomaly of mass gain
. We anticipate our highly resolved estimates to advance the understanding of drivers that govern the distribution of glacier change, and to extend our capabilities of predicting these changes at all scales. Predictions robustly benchmarked against observations are critically needed to design adaptive policies for the local- and regional-scale management of water resources and cryospheric risks, as well as for the global-scale mitigation of sea-level rise.
The causes of sea-level rise since 1900 Frederikse, Thomas; Landerer, Felix; Caron, Lambert ...
Nature (London),
08/2020, Letnik:
584, Številka:
7821
Journal Article
Recenzirano
The rate of global-mean sea-level rise since 1900 has varied over time, but the contributing factors are still poorly understood
. Previous assessments found that the summed contributions of ice-mass ...loss, terrestrial water storage and thermal expansion of the ocean could not be reconciled with observed changes in global-mean sea level, implying that changes in sea level or some contributions to those changes were poorly constrained
. Recent improvements to observational data, our understanding of the main contributing processes to sea-level change and methods for estimating the individual contributions, mean another attempt at reconciliation is warranted. Here we present a probabilistic framework to reconstruct sea level since 1900 using independent observations and their inherent uncertainties. The sum of the contributions to sea-level change from thermal expansion of the ocean, ice-mass loss and changes in terrestrial water storage is consistent with the trends and multidecadal variability in observed sea level on both global and basin scales, which we reconstruct from tide-gauge records. Ice-mass loss-predominantly from glaciers-has caused twice as much sea-level rise since 1900 as has thermal expansion. Mass loss from glaciers and the Greenland Ice Sheet explains the high rates of global sea-level rise during the 1940s, while a sharp increase in water impoundment by artificial reservoirs is the main cause of the lower-than-average rates during the 1970s. The acceleration in sea-level rise since the 1970s is caused by the combination of thermal expansion of the ocean and increased ice-mass loss from Greenland. Our results reconcile the magnitude of observed global-mean sea-level rise since 1900 with estimates based on the underlying processes, implying that no additional processes are required to explain the observed changes in sea level since 1900.
PDF
