Initial carbonate weathering is linked with vegetation development along a 127-year glacial retreat chronosequence in the subtropical high mountainous Hailuogou region (SW China)

Aims The retreat of glaciers is exposing new terrains to primary plant succession around the globe. To improve the understanding of vegetation development along a glacier retreat chronosequence, we (i) evaluated a possible link between base metal (Ca, Mg, K, Na) supply and vegetation establishment, (ii) determined the rates of the establishment of soil and plant base metal stocks, and (iii) estimated the size of the main base metal fluxes. Methods We determined base metal stocks in the soil organic layer, the mineral topsoil (0–10 cm), and in leaves/needles, trunk, bark, branches and roots of the dominating shrub and tree species and estimated fluxes of atmospheric deposition, plant uptake and leaching losses along the 127-yr Hailuogou chronosequence. Results Total ecosystem Ca and Mg stocks decreased along the chronosequence, while those of K and Na were unrelated with ecosystem age. Fortyfour and 30% of the initial stocks of Ca and Mg, respectively, were leached during the first 47 years, at rates of 130 ± 10.6 g m−2 year−1 Ca and 35 ± 3.1 g m−2 year−1 Mg. The organic layer accumulated at a mean rate of 288 g m−2 year−1 providing a bioavailable base metal stock, which was especially important for K cycling. Conclusions We suggest that the initial high Ca bioavailability because of a moderately alkaline soil pH and carbonate depletion in 47 years, together with the dissolution of easily-weatherable silicates providing enough Mg and K to the pioneer vegetation, contributed to the establishment of the mature forest in ca. 80 years.

Glacio-lacustrine sedimentation in newly discovered paleo-lakes, Westland, New Zealand

<p>The remnant effects of Quaternary glaciation dominate the geomorphology of South Westland, New Zealand. Well-constrained glaciogenic records for the Last Glacial Maximum (LGM) (~MIS 2) show ice to have extended significant distances across the Westland piedmont, becoming tidewater calving in places. Despite clear evidence for glacial advance, landscape response to glacial retreat remains relatively poorly understood, with few described sedimentary sequences clearly recording deglaciation processes. A 240-metre thick glacio-lacustrine sedimentary sequence intercepted by drilling in the Whataroa Valley (DFDP-2) provides the first compelling evidence of pro-glacial lake formation in response to glacial retreat in Westland. To understand the vertical facies succession observed in this sequence, two glacio-lacustrine facies schemes and depositional models were developed. To do this, previously unmapped glacio-lacustrine sedimentary sequences in the Westland region underwent detailed sedimentological analysis to identify key glacio-lacustrine facies. In the Waitangitaona and Arahura river valleys, the presence of glacio-lacustrine sequences is also used to mark paleo-lake formation in the respective catchments. Using the facies scheme and depositional models, together with 14C chronology and sedimentological analysis, a series of conclusions are developed from the DFDP-2 sequence: 1) Deposition occurred in an over-deepened glacial trough, with the sequence consisting of a basal diamictite, overlain by a ~ 140-metre interval of lacustrine siltstones and sandstones. 2) The lower ~ 180-metres of sediment accumulated in 659 ± 151 yrs between 16609 ± 151 and 15994 ± 94 cal. yr BP, as the depositional environment at the drill-site evolved from an ice contact to an ice distal lacustrine setting. 3) Extremely rapid sedimentation rates, as well as high lake levels allowed the preservation of glacially over-steepened bedrock slopes beneath the Whataroa Valley. The formation of a previously unknown, ~190 km2 pro-glacial lake on the Whataroa piedmont is inferred from the DFDP-2 sequence, with lake formation causing accelerated glacial retreat from the late LGM maxima. The presence of several catchments with comparable piedmont geometry suggests pro-glacial lake formation may have been a common response to glacial retreat in Westland. For a period, pro-glacial lakes may have been a significant transitory feature on the Westland landscape.</p>

Glacio-lacustrine sedimentation in newly discovered paleo-lakes, Westland, New Zealand

<p>The remnant effects of Quaternary glaciation dominate the geomorphology of South Westland, New Zealand. Well-constrained glaciogenic records for the Last Glacial Maximum (LGM) (~MIS 2) show ice to have extended significant distances across the Westland piedmont, becoming tidewater calving in places. Despite clear evidence for glacial advance, landscape response to glacial retreat remains relatively poorly understood, with few described sedimentary sequences clearly recording deglaciation processes. A 240-metre thick glacio-lacustrine sedimentary sequence intercepted by drilling in the Whataroa Valley (DFDP-2) provides the first compelling evidence of pro-glacial lake formation in response to glacial retreat in Westland. To understand the vertical facies succession observed in this sequence, two glacio-lacustrine facies schemes and depositional models were developed. To do this, previously unmapped glacio-lacustrine sedimentary sequences in the Westland region underwent detailed sedimentological analysis to identify key glacio-lacustrine facies. In the Waitangitaona and Arahura river valleys, the presence of glacio-lacustrine sequences is also used to mark paleo-lake formation in the respective catchments. Using the facies scheme and depositional models, together with 14C chronology and sedimentological analysis, a series of conclusions are developed from the DFDP-2 sequence: 1) Deposition occurred in an over-deepened glacial trough, with the sequence consisting of a basal diamictite, overlain by a ~ 140-metre interval of lacustrine siltstones and sandstones. 2) The lower ~ 180-metres of sediment accumulated in 659 ± 151 yrs between 16609 ± 151 and 15994 ± 94 cal. yr BP, as the depositional environment at the drill-site evolved from an ice contact to an ice distal lacustrine setting. 3) Extremely rapid sedimentation rates, as well as high lake levels allowed the preservation of glacially over-steepened bedrock slopes beneath the Whataroa Valley. The formation of a previously unknown, ~190 km2 pro-glacial lake on the Whataroa piedmont is inferred from the DFDP-2 sequence, with lake formation causing accelerated glacial retreat from the late LGM maxima. The presence of several catchments with comparable piedmont geometry suggests pro-glacial lake formation may have been a common response to glacial retreat in Westland. For a period, pro-glacial lakes may have been a significant transitory feature on the Westland landscape.</p>

Studies on the glaciovolcanic and magmatic evolution of Ruapehu Volcano, New Zealand

<p>This thesis undertakes a detailed case study of the processes and timescales of arc andesite-dacite magma generation and lava flow emplacement at a continental composite volcano. This has been achieved through the collection and integration of high-resolution field, geochronological and geochemical datasets for lava flows that form the edifice of Ruapehu. The influence of syn-eruptive lava-ice interaction on the distribution and preservation of lava flows on glaciated composite volcanoes is investigated by characterising the morphology and fracture characteristics of effusive products at Ruapehu. Ice-bounded and ice-dammed lava flows display over-thickened (50–100 m-high) margins adjacent to or within glaciated valleys, are intercalated with till and have lateral margins that are pervasively fractured by quench-contraction cooling joints. These characteristics can be accounted for by impoundment and chilling of lava flows that were emplaced against large flank glaciers. In contrast, lava flows located within valleys have minimal moraine cover and glacial striae and are characterised by fracture networks indicative of only localised and minor interaction with ice/snow. These lavas were emplaced onto a relatively ice-free edifice following glacial retreat since ~18 ka. New high-precision ⁴⁰Ar/³⁹Ar eruption ages and whole-rock major element geochemistry for lava flows are interpreted in the context of geologic mapping, volcano-ice interaction processes and previous chronostratigraphic studies. This provides a high-resolution eruptive history and edifice evolution model for Ruapehu. Sub-glacial to ice-marginal effusive eruption of basaltic-andesite and andesite constructed the northern portion of the exposed edifice between ~200 and 150 ka (Te Herenga Formation) and the wide southeastern planèze as well as parts of the northern, eastern and western flanks of Ruapehu between ~166 and 80 ka (Wahianoa Formation). No ages were returned for lava flows for the period from 80–50 ka, indicating one or a combination of: an eruptive hiatus; subsequent erosion and burial of lavas; or syn-eruptive glacial conveyance of lava flows to the ring-plain. The greater part of the modern edifice was constructed via effusion of lava flows of the syn-glacial Mangawhero Formation (50–15 ka) and post-glacial Whakapapa Formation (<15 ka). Syn-glacial edifice growth occurred primarily via effusion of andesite-dacite lava flows that formed ice-bounded ridges adjacent to valleyfilling glaciers. Post-glacial summit cones were constructed in the presence of remnant upper flank glaciers between 15 and 10 ka. Debuttressing of two northern summit cones and a southern summit cone as ice underwent continued post-glacial retreat resulted in two major Holocene sector collapses and deposition of debris avalanche deposits on the northern and south-eastern flanks of Ruapehu, respectively. The northern collapse scar was infilled by a new cone comprising <10 ka lava flows that form the modern upper northern and eastern flanks of the volcano. Late Holocene to historic eruptive activity has occurred through Crater Lake, which occupies the site of the collapsed southern cone. New whole-rock major and trace element compositions for lavas and their mineral and melt inclusion geochemical characteristics are evaluated within the context of the improved chronostratigraphic framework. The new constraints are combined with existing whole-rock isotopic data to establish the long-term development of the magma generation system beneath Ruapehu. Basaltic-andesite lavas erupted between ~200 and 150 ka contain low-K₂O (2–3 wt. %) melt inclusions and have whole-rock compositions characterised by low incompatible element (K, Rb, Ba, Th, U) abundances and high ¹⁴³Nd/¹⁴⁴Nd-low ⁸⁷Sr/⁸⁶Sr when compared to younger eruptive products. In particular, basaltic-andesite to dacite lavas that were erupted between 50–35 ka define a high-K/Ca trend over a range of ~8 wt. % SiO₂ as well as elevated incompatible trace element contents when compared to all other documented eruptive products from Ruapehu. Rhyodacitic to rhyolitic melt inclusions, interstitial glass and melt pockets in partially fused feldspathic xenoliths contained within the dacite lavas from this latter period contain high K₂O (5–6 wt. %) and Rb contents (250–280 ppm). The whole-rock and glass characteristics of 50–35 ka lavas reflect the generation and assimilation of partial melts of the greywacke-argillite basement within the magma system beneath Ruapehu during this period. Selective partial melting and assimilation of fertile, K- and Rb-rich mineral phases (e.g. biotite) within the meta-sedimentary mineral assemblage is inferred to explain the enriched nature of these melts. A reversion to progressively less silicic and less potassic lavas with lower incompatible element abundances erupted since 26 ka is matched by the recurrent incorporation of crystals that trapped low-K₂O melt inclusions. The trend is interpreted to reflect the exhaustion of fertile phases within assimilated continental source rocks as the crust was progressively heated during long-term thermal conditioning of the arc lithosphere beneath Ruapehu.</p>

Studies on the glaciovolcanic and magmatic evolution of Ruapehu Volcano, New Zealand

<p>This thesis undertakes a detailed case study of the processes and timescales of arc andesite-dacite magma generation and lava flow emplacement at a continental composite volcano. This has been achieved through the collection and integration of high-resolution field, geochronological and geochemical datasets for lava flows that form the edifice of Ruapehu. The influence of syn-eruptive lava-ice interaction on the distribution and preservation of lava flows on glaciated composite volcanoes is investigated by characterising the morphology and fracture characteristics of effusive products at Ruapehu. Ice-bounded and ice-dammed lava flows display over-thickened (50–100 m-high) margins adjacent to or within glaciated valleys, are intercalated with till and have lateral margins that are pervasively fractured by quench-contraction cooling joints. These characteristics can be accounted for by impoundment and chilling of lava flows that were emplaced against large flank glaciers. In contrast, lava flows located within valleys have minimal moraine cover and glacial striae and are characterised by fracture networks indicative of only localised and minor interaction with ice/snow. These lavas were emplaced onto a relatively ice-free edifice following glacial retreat since ~18 ka. New high-precision ⁴⁰Ar/³⁹Ar eruption ages and whole-rock major element geochemistry for lava flows are interpreted in the context of geologic mapping, volcano-ice interaction processes and previous chronostratigraphic studies. This provides a high-resolution eruptive history and edifice evolution model for Ruapehu. Sub-glacial to ice-marginal effusive eruption of basaltic-andesite and andesite constructed the northern portion of the exposed edifice between ~200 and 150 ka (Te Herenga Formation) and the wide southeastern planèze as well as parts of the northern, eastern and western flanks of Ruapehu between ~166 and 80 ka (Wahianoa Formation). No ages were returned for lava flows for the period from 80–50 ka, indicating one or a combination of: an eruptive hiatus; subsequent erosion and burial of lavas; or syn-eruptive glacial conveyance of lava flows to the ring-plain. The greater part of the modern edifice was constructed via effusion of lava flows of the syn-glacial Mangawhero Formation (50–15 ka) and post-glacial Whakapapa Formation (<15 ka). Syn-glacial edifice growth occurred primarily via effusion of andesite-dacite lava flows that formed ice-bounded ridges adjacent to valleyfilling glaciers. Post-glacial summit cones were constructed in the presence of remnant upper flank glaciers between 15 and 10 ka. Debuttressing of two northern summit cones and a southern summit cone as ice underwent continued post-glacial retreat resulted in two major Holocene sector collapses and deposition of debris avalanche deposits on the northern and south-eastern flanks of Ruapehu, respectively. The northern collapse scar was infilled by a new cone comprising <10 ka lava flows that form the modern upper northern and eastern flanks of the volcano. Late Holocene to historic eruptive activity has occurred through Crater Lake, which occupies the site of the collapsed southern cone. New whole-rock major and trace element compositions for lavas and their mineral and melt inclusion geochemical characteristics are evaluated within the context of the improved chronostratigraphic framework. The new constraints are combined with existing whole-rock isotopic data to establish the long-term development of the magma generation system beneath Ruapehu. Basaltic-andesite lavas erupted between ~200 and 150 ka contain low-K₂O (2–3 wt. %) melt inclusions and have whole-rock compositions characterised by low incompatible element (K, Rb, Ba, Th, U) abundances and high ¹⁴³Nd/¹⁴⁴Nd-low ⁸⁷Sr/⁸⁶Sr when compared to younger eruptive products. In particular, basaltic-andesite to dacite lavas that were erupted between 50–35 ka define a high-K/Ca trend over a range of ~8 wt. % SiO₂ as well as elevated incompatible trace element contents when compared to all other documented eruptive products from Ruapehu. Rhyodacitic to rhyolitic melt inclusions, interstitial glass and melt pockets in partially fused feldspathic xenoliths contained within the dacite lavas from this latter period contain high K₂O (5–6 wt. %) and Rb contents (250–280 ppm). The whole-rock and glass characteristics of 50–35 ka lavas reflect the generation and assimilation of partial melts of the greywacke-argillite basement within the magma system beneath Ruapehu during this period. Selective partial melting and assimilation of fertile, K- and Rb-rich mineral phases (e.g. biotite) within the meta-sedimentary mineral assemblage is inferred to explain the enriched nature of these melts. A reversion to progressively less silicic and less potassic lavas with lower incompatible element abundances erupted since 26 ka is matched by the recurrent incorporation of crystals that trapped low-K₂O melt inclusions. The trend is interpreted to reflect the exhaustion of fertile phases within assimilated continental source rocks as the crust was progressively heated during long-term thermal conditioning of the arc lithosphere beneath Ruapehu.</p>

Post-LGM glacial retreat and Early Holocene monsoon intensification drives aggradation in the interiors of the Kashmir Himalaya

Understanding the response of glaciated catchments to climate change is crucial for assessing sediment transport from the high-elevation, semi-arid sectors in the Himalaya. The fluvioglacial sediments stored in the semi-arid Padder valley in the Kashmir Himalaya record valley aggradation during ~20 -10 ka. We relate the initial stage of valley aggradation to increased sediment supply from the deglaciated catchment during the glacial-to-interglacial phase transition. Previously-published bedrock-exposure ages in the upper Chenab River valley suggest ~180 km retreat of the valley glacier during ~20 - 15 ka. Increasing roundness of sand-grains and reducing mean grain-size from the bottom to the top of the valley-fill sequence hint about increasing fluvial transport with time and corroborate with the glacial retreat history. The later stages of aggradation can be attributed to strong monsoon during the early Holocene. Especially, the hillslope debris that drapes the fluvioglacial sediment archive may have resulted from the early Holocene monsoon maximum. We observe a net degradation of the valley-fill in the Holocene reflecting the weakening of summer monsoon or reduced input from the glaciers. Our study highlights the coupled effect of deglaciation and monsoon intensification in sediment transfer from the high-elevation sectors of the Himalaya.

Supplemental Material: Late Pleistocene and early Holocene sea-level history and glacial retreat interpreted from shell-bearing marine deposits of southeastern Alaska, USA

<div>Shell-bearing strata dataset from southeastern Alaska.<br></div>

Supplemental Material: Late Pleistocene and early Holocene sea-level history and glacial retreat interpreted from shell-bearing marine deposits of southeastern Alaska, USA

<div>Shell-bearing strata dataset from southeastern Alaska.<br></div>

Post-LGM glacial retreat drives aggradation in the interiors of the Kashmir Himalaya

Understanding the response of glaciated catchments to climate change is fundamental for assessing sediment transport from the high-elevation, semi-arid to arid sectors in the Himalaya to the foreland basin. The fluvioglacial sediments stored in the semi-arid Padder valley in the Kashmir Himalaya record valley aggradation during ~19-11 ka. We relate the valley aggradation to increased sediment supply from the deglaciated catchment during the glacial-to-interglacial phase transition. Previously-published bedrock-exposure ages in the upper Chenab valley suggest ~180 km retreat of the valley glacier during ~20-15 ka. Increasing roundness of sand-grains and reducing mean grain-size from the bottom to the top of the valley-fill sequence hint about increasing fluvial transport with time and corroborate with the glacial retreat history. Our result also correlates well with late Pleistocene-early Holocene sediment aggradation observed across most Western Himalayan valleys. It highlights the spatiotemporal synchronicity of sediment transfer from the Himalayas triggered by climate change.

The glacial history of Rocky Top cirque, southeast Fiordland, New Zealand

<p><b>Understanding natural climate variability is a fundamental goal of paleoclimate science. Temperate mountain glaciers are sensitive to climate variability, changing volume, and thus thickness and length, in response to changes in temperature and precipitation. Glaciers deposit moraines at their margins, which if well-preserved may provide evidence of glacier length fluctuations following glacial retreat. Therefore mountain glaciers can be used as proxies to investigate past climatic changes, offering the potential to reconstruct the timing and magnitude of natural climate variability and paleoclimate for the former glacier extent(s). </b></p><p>This study applies methods of detailed geomorphological mapping and cosmogenic 10Be surface exposure dating to establish a high-precision moraine chronology and examine the timing and magnitude of glacier length changes at Rocky Top cirque. A quantitative reconstruction of paleoclimate for the identified former glacier extents was produced using an equilibrium-line altitude (ELA) reconstruction method and application of a temperature lapse rate. Findings show a clear pattern of glacial retreat at the end of the Last Glacial Maximum, with exposure ages from moraine boulders successfully constraining the timing of five distinct periods of glacier readvance or standstills. The most recent glacial event at Rocky Top cirque occurred between 17342 ± 172 yrs BP and during this period the ELA was depressed by 611 m. The second innermost moraine produced an indistinguishable age of 17196 ± 220 yrs BP and had an ELA depression of 616 m, indicating rapid glacial retreat. Progressively older moraines produced surface exposure ages of 18709 ± 237 and 19629 ± 308 yrs BP, with ELA depressions of 618 and 626 m respectively. The oldest moraine of 34608 ± 8437 yrs BP had insufficient geomorphic constraint to produce an ELA. Paleoclimate reconstruction results suggest that a best estimate of paleotemperature at the time of moraine formation (~19-17 ka) was between 3.2 ± 0.8 to 3.3 ± 0.8°C cooler than present-day. </p><p>Net retreat of the former glacier is consistent with other similar moraine chronologies from the Southern Alps, which supports the regional trend and suggests that glaciers in the Southern Alps responded to common climatic forcings between ~19-17 ka. </p>