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ABSTRACT Glacial marine sediment deposition varies both spatially and temporally, but nearly all studies evaluate down-core (∼ time) variations in sediment variables with little consideration for across core variability, or even the consistency of a data set over distance scales of 1 to 1000 m. Grain size and quantitative X-ray diffraction (qXRD) methods require only ≤ 1 g of sediment and thus analyses assume that the identification of coarse sand (i.e., ice-rafted debris) and sediment mineral composition are representative of the depth intervals. This assumption was tested for grain size and mineral weight % on core MD99-2317, off East Greenland. Samples were taken from two sections of the core that had contrasting coarse-sand content. A total of fourteen samples were taken consisting of seven (vertical) and two (horizontal) samples, with five replicates per sample for qXRD analyses and ∼ 10 to 20 replicates for grain size. They had an average dry weight of 10.5 ± 0.5 g and are compared with two previous sets of sediment samples that averaged 54.1 ± 18.9 g and 20.77 ± 5.8 g dry weight. The results indicated some significant differences between the pairs of samples for grain-size parameters (mean sortable silt, and median grain size) but little difference in the estimates of mineral weight percentages. Out of 84 paired mineral and grain-size comparisons only 17 were significantly different at p = < 0.05 in the post-hoc Scheffe test, all of which were linked to grain-size attributes. 

Abstract. Most extant ice caps mantling low-relief Arctic Canada landscapes remained cold based throughout the late Holocene, preserving in situ bryophytes killed as ice expanded across vegetated landscapes. After reaching peak late Holocene dimensions ∼1900 CE, ice caps receded as Arctic summers warmed, exposing entombed vegetation. The calibrated radiocarbon ages of entombed moss collected near ice cap margins (kill dates) define when ice advanced across the site, killing the moss, and remained over the site until the year of their collection. In an earlier study, we reported 94 last millennium radiocarbon dates on in situ dead moss collected at ice cap margins across Baffin Island, Arctic Canada. Tight clustering of those ages indicated an abrupt onset of the Little Ice Age at ∼1240 CE and further expansion at ∼1480 CE coincident with episodes of major explosive volcanism. Here we test the confidence in kill dates as reliable predictors of expanding ice caps by resampling two previously densely sampled ice complexes ∼15 years later after ∼250 m of ice recession. The probability density functions (PDFs) of the more recent series of ages match PDFs of the earlier series but with a larger fraction of early Common Era ages. Post 2005 CE ice recession has exposed relict ice caps that grew during earlier Common Era advances and were preserved beneath later ice cap growth. We compare the 106 kill dates from the two ice complexes with 80 kill dates from 62 other ice caps within 250 km of the two densely sampled ice complexes. The PDFs of kill dates from the 62 other ice caps cluster in the same time windows as those from the two ice complexes alone, with the PDF of all 186 kill dates documenting episodes of widespread ice expansion restricted almost exclusively to 250–450 CE, 850–1000 CE, and a dense early Little Ice Age cluster with peaks at ∼1240 and ∼1480 CE. Ice continued to expand after 1480 CE, reaching maximum dimensions at ∼1880 CE that are still visible as zones of sparse vegetation cover in remotely sensed imagery. Intervals of widespread ice cap expansion coincide with persistent decreases in mean summer surface air temperature for the region in a Community Earth System Model (CESM) fully coupled Common Era simulation, suggesting the primary forcings of the observed snowline lowering were both modest declines in summer insolation and cooling resulting from explosive volcanism, most likely intensified by positive feedbacks from increased snow cover and sea ice and reduced northward heat transport by the oceans. The clusters of ice cap expansion defined by moss kill dates are mirrored in an annually resolved Common Era record of ice cap dimensions in Iceland, suggesting this is a circum-North-Atlantic–Arctic climate signal for the Common Era. During the coldest century of the Common Era, 1780–1880 CE, ice caps mantled >11 000 km2 of north-central Baffin Island, whereas <100 km2 is glaciated at present. The peak Little Ice Age state approached conditions expected during the inception phase of an ice age and was only reversed after 1880 CE by anthropogenic alterations of the planetary energy balance. 

Abstract. Strong similarities in Holocene climate reconstructions derived from multipleproxies (BSi, TOC – total organic carbon, δ13C, C∕N, MS – magnetic susceptibility, δ15N)preserved in sediments from both glacial and non-glacial lakes across Icelandindicate a relatively warm early to mid Holocene from 10 to 6 ka,overprinted with cold excursions presumably related to meltwater impact onNorth Atlantic circulation until 7.9 ka. Sediment in lakes from glacialcatchments indicates their catchments were ice-free during this interval.Statistical treatment of the high-resolution multi-proxy paleoclimate lakerecords shows that despite great variability in catchment characteristics,the sediment records document more or less synchronous abrupt, colddepartures as opposed to the smoothly decreasing trend in Northern Hemispheresummer insolation. Although all lake records document a decline in summertemperature through the Holocene consistent with the regular decline insummer insolation, the onset of significant summer cooling occurs ∼5 ka at high-elevation interior sites but is variably later at sitescloser to the coast, suggesting that proximity to the sea may modulate the impactfrom decreasing summer insolation. The timing of glacier inception during themid Holocene is determined by the descent of the equilibrium line altitude(ELA), which is dominated by the evolution of summer temperature as summerinsolation declined as well as changes in sea surface temperature for coastalglacial systems. The glacial response to the ELA decline is also highlydependent on the local topography. The initial ∼5 ka nucleation ofLangjökull in the highlands of Iceland defines the onset of neoglaciationin Iceland. Subsequently, a stepwise expansion of both Langjökull andnortheast Vatnajökull occurred between 4.5 and 4.0 ka, with a secondabrupt expansion ∼3 ka. Due to its coastal setting and lowertopographic threshold, the initial appearance of Drangajökull in the NWof Iceland was delayed until ∼2.3 ka. All lake records reflect abruptsummer temperature and catchment disturbance at ∼4.5 ka, statisticallyindistinguishable from the global 4.2 ka event, and a second widespreadabrupt disturbance at 3.0 ka, similar to the stepwise expansion ofLangjökull and northeast Vatnajökull. Both are intervalscharacterized by large explosive volcanism and tephra distribution in Icelandresulting in intensified local soil erosion. The most widespread increase in glacier advance, landscapeinstability, and soil erosion occurred shortly after 2 ka, likely due to acomplex combination of increased impact from volcanic tephra deposition,cooling climate, and increased sea ice off the coast of Iceland. All lakerecords indicate a strong decline in temperature ∼1.5 ka, whichculminated during the Little Ice Age (1250–1850 CE) when the glaciersreached their maximum Holocene dimensions.