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Abstract: This paper presents new Holocene relative sea-level (RSL) data collected from isolation basins close to the town of Paamiut in south west Greenland. The data shows a rapid fall from a marine limit of c. 52 m asl at c. 10.9 cal. ka BP to close to present by c. 9.5 cal. ka BP, at rates of up to c. 32 mm/yr, falling below present for the majority of the Holocene before rising to present in the last 2000 years. The elevation of the RSL lowstand is not well constrained, but was at least below −3 m. This pattern of rapid RSL fall during the early Holocene matches the pattern seen at other southern Greenland locations suggesting rapid, largely simultaneous ice retreat from the area surrounding the Qassimiut Lobe at the start of the Holocene, occurring c. 2000 years after the initial deglaciation of the extreme southern tip of Greenland. The RSL histories from this and other southern Greenland locations are distinct to those recorded further north along the west coast, and are in broad agreement with a pattern of vertical land motion and RSL predicted by the Huy2 model (Simpson et al., 2009), which predicts an 80 m drop in the contribution of vertical land motion to RSL at 10 cal. ka BP between Sisimiut and Paamiut on the west coast. Despite this broad-scale spatial agreement between the RSL data and the Huy2 model, it fails to satisfactorily predict the Holocene RSL histories at Paamiut and other southern Greenland locations. Sensitivity tests indicate that the data-model misfits are most likely due to an over-estimate of the forcing during the Holocene Thermal Maximum (or the response to this forcing) in southern Greenland and error in the North American ice sheets component of the background deglaciation model. Our new data suggests that much of the southern part of the ice sheet acted differently to the area further north. However RSL changes at Paamiut are also largely impacted by regional and larger-scale processes including a bulls-eye of uplift centred on the west, the impact of the Holocene Thermal Maximum and the influence of the collapse of the North American ice sheets. [Copyright &y& Elsevier]

Abstract: This paper presents new evidence regarding relative sea-level (RSL) changes and vertical land motions at three sites in Greenland since 1300A.D., a time interval that spans the later part of the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA). We observe RSL rise at two sites in central west Greenland from c. −0.80±0.20m at c. 1300A.D. to c. −0.20m±0.25m at c. 1600A.D., after which RSL slowed and then stabilised. At a third site in south Greenland, we observe RSL rise from c. −1.40±0.20m at c. 1400A.D. until c. 1750A.D., after which RSL slowed and was stable during at least the latter part of the 20th century. The c. 1600A.D. RSL slow-down seen at the two former sites is surprising because it occurs during the LIA when one might expect the ice sheet to be gaining mass and causing RSL to rise. We interpret this RSL slowdown to indicate a period of enhanced regional mass loss from central west Greenland since c. 1600A.D. and propose two hypotheses for this loss: first, a reduction in precipitation during cold and dry conditions and second, higher air temperatures and increased peripheral surface melt of the ice sheet from this date onwards. The latter hypothesis is compatible with a well-established temperature seesaw between western Greenland and northern Europe and, potentially, a previously identified shift from a positive to generally more negative NAO conditions around 1400 to 1600A.D. Our study shows how RSL data from Greenland can provide constraints on the timing of ice sheet fluctuations in the last millennium and challenges the notion that during cold periods in northern Europe the ice sheet in west Greenland gained mass. [Copyright &y& Elsevier]

Abstract: Isolation basins are natural topographic depressions that at various times in their history may be connected to or isolated from the sea by changes in relative sea-level (RSL). They provide a valuable source of data for tracking large scale (tens of meters) changes in RSL over millennia, as well as quiet-water depositional environments where abrupt changes caused by tsunami, iceberg roll or storms may be recorded. In this paper we review isolation basins as sources of RSL data with a particular focus on their use in Greenland to constrain the Holocene history of the ice sheet. A new RSL curve from Disko Fjord, West Greenland is presented, which shows that local ice free conditions were established at c. 11 k cal yr BP, after which RSL fell rapidly from a marine limit at c. 80 m to reach close to present sea level by c. 4 k cal yr BP. We compare this record with other isolation basin RSL data from six other sites in Disko Bugt and note a strong northwest/southeast differential rebound across the area during the early and mid-Holocene that reflects variations in ice load history. We compare the Disko Bugt data with other previously published isolation basin RSL records from Sisimiut (central West Greenland), Nanortalik (south Greenland) and Ammassalik (southeast Greenland). RSL fell below present during the early-Holocene at Nanortalik (c. 10 k cal yr BP) and during the mid to late Holocene elsewhere before rising to present. These differences reflect variations in the timing and amount of Greenland ice load change since the last glacial maximum, as well as non-Greenland processes, notably the collapse of the Laurentide forebulge and also changes in ice equivalent sea-level. Isolation basin data have relatively small age and height uncertainties compared with other RSL indicators, enabling them to resolve between different earth and ice sheet models, especially during periods of large ice load and RSL change. [Copyright &y& Elsevier]

An ice sheet model was constrained to reconstruct the evolution of the Greenland Ice Sheet (GrIS) from the Last Glacial Maximum (LGM) to present to improve our understanding of its response to climate change. The study involved applying a glaciological model in series with a glacial isostatic adjustment and relative sea-level (RSL) model. The model reconstruction builds upon the work of Simpson et al. (2009) through four main extensions: (1) a larger constraint database consisting of RSL and ice extent data; model improvements to the (2) climate and (3) sea-level forcing components; (4) accounting for uncertainties in non-Greenland ice. The research was conducted primarily to address data-model misfits and to quantify inherent model uncertainties with the Earth structure and non-Greenland ice. Our new model (termed Huy3) fits the majority of observations and is characterised by a number of defining features. During the LGM, the ice sheet had an excess of 4.7 m ice-equivalent sea-level (IESL), which reached a maximum volume of 5.1 m IESL at 16.5 cal ka BP. Modelled retreat of ice from the continental shelf progressed at different rates and timings in different sectors. Southwest and Southeast Greenland began to retreat from the continental shelf by ∼16 to 14 cal ka BP, thus responding in part to the Bølling-Allerød warm event (c. 14.5 cal ka BP); subsequently ice at the southern tip of Greenland readvanced during the Younger Dryas cold event. In northern Greenland the ice retreated rapidly from the continental shelf upon the climatic recovery out of the Younger Dryas to present-day conditions. Upon entering the Holocene (11.7 cal ka BP), the ice sheet soon became land-based. During the Holocene Thermal Maximum (HTM; 9-5 cal ka BP), air temperatures across Greenland were marginally higher than those at present and the GrIS margin retreated inland of its present-day southwest position by 40–60 km at 4 cal ka BP which produced a deficit volume of 0.16 m IESL relative to present. In response to the HTM warmth, our optimal model reconstruction lost mass at a maximum centennial rate of c. 103.4 Gt/yr. Our results suggest that remaining data-model discrepancies are affiliated with missing physics and sub-grid processes of the glaciological model, uncertainties in the climate forcing, lateral Earth structure, and non-Greenland ice (particularly the North American component). Finally, applying the Huy3 Greenland reconstruction with our optimal Earth model we generate present-day uplift rates across Greenland due to past changes in the ocean and ice loads with explicit error bars due to uncertainties in the Earth structure. Present-day uplift rates due to past changes are spatially variable and range from 3.5 to −7 mm/a (including Earth model uncertainty). [ABSTRACT FROM AUTHOR]

In the Northern Hemisphere, an insolation driven Early to Middle Holocene Thermal Maximum was followed by a Neoglacial cooling that culminated during the Little Ice Age (LIA). Here, we review the glacier response to this Neoglacial cooling in Greenland. Changes in the ice margins of outlet glaciers from the Greenland Ice Sheet as well as local glaciers and ice caps are synthesized Greenland-wide. In addition, we compare temperature reconstructions from ice cores, elevation changes of the ice sheet across Greenland and oceanographic reconstructions from marine sediment cores over the past 5,000 years. The data are derived from a comprehensive review of the literature supplemented with unpublished reports. Our review provides a synthesis of the sensitivity of the Greenland ice margins and their variability, which is critical to understanding how Neoglacial glacier activity was interrupted by the current anthropogenic warming. We have reconstructed three distinct periods of glacier expansion from our compilation: two older Neoglacial advances at 2,500 – 1,700 yrs. BP (Before Present = 1950 CE, Common Era) and 1,250 – 950 yrs. BP; followed by a general advance during the younger Neoglacial between 700-50 yrs. BP, which represents the LIA. There is still insufficient data to outline the detailed spatio-temporal relationships between these periods of glacier expansion. Many glaciers advanced early in the Neoglacial and persisted in close proximity to their present-day position until the end of the LIA. Thus, the LIA response to Northern Hemisphere cooling must be seen within the wider context of the entire Neoglacial period of the past 5,000 years. Ice expansion appears to be closely linked to changes in ice sheet elevation, accumulation, and temperature as well as surface-water cooling in the surrounding oceans. At least for the two youngest Neoglacial advances, volcanic forcing triggering a sea-ice /ocean feedback, could explain their initiation. There are probably several LIA glacier fluctuations since the first culmination close to 1250 CE (Common Era) and available data suggests ice culminations in the 1400s, early to mid-1700s and early to mid-1800s CE. The last LIA maxima lasted until the present deglaciation commenced around 50 yrs. BP (1900 CE). The constraints provided here on the timing and magnitude of LIA glacier fluctuations delivers a more realistic background validation for modelling future ice sheet stability. [ABSTRACT FROM AUTHOR]