A5: Grafton Notch State Park: Glacial Gorges and Streams Under Pressure in the Mahoosic Range, Maine

Guidebook for field trips in Western Maine and Northern New Hampshire: New England Intercollegiate Geological Conference, p. 95-104

The Last Glacial Maximum in Central North Island, New Zealand: Palaeoclimate Inferences from Glacier Modelling

Quantitative palaeoclimate reconstructions provide data for evaluating the mechanisms of past, natural climate variability. Geometries of former mountain glaciers constrained by moraine mapping afford the opportunity to reconstruct palaeoclimate, due to the close relationship between ice extent and local climate. In this study, we present results from a series of experiments using a 2D coupled energy-balance/ice-flow model that investigate the palaeoclimate significance of Last Glacial Maximum m oraines within nine catchments in the central North Island, New Zealand. We find that the former ice limits can be simulated when present-day temperatures are reduced by between 4 and 7 ◦C, if precipitation remains unchanged from present. The spread in the results between the nine catchments is likely to rep- resent the combination of chronological and model uncer- tainties. The majority of catchments targeted require tem- perature decreases of 5.1 to 6.3 ◦ C to simulate the former glaciers, which represents our best estimate of the tempera- ture anomaly in the central North Island, New Zealand, dur- ing the Last Glacial Maximum. A decrease in precipitation of up to 25 % from present, as suggested by proxy evidence and climate models, increases the magnitude of the required temperature changes by up to 0.8 ◦ C. Glacier model experi- ments using reconstructed topographies that exclude the vol- ume of post-glacial (\u3c 15 ka) volcanism generally increased the magnitude of cooling required to simulate the former ice limits by up to 0.5 ◦ C. Our palaeotemperature estimates ex- pand the spatial coverage of proxy-based quantitative palaeo- climate reconstructions in New Zealand. Our results are also consistent with independent, proximal temperature recon- structions from fossil groundwater and pollen assemblages, as well as similar glacier modelling reconstructions from the central Southern Alps, which suggest air temperatures were ca. 6 ◦ C lower than present across New Zealand during the Last Glacial Maximum

Evaluation of Lateglacial temperatures in the Southern Alps of New Zealand based on glacier modelling at Irishman Stream, Ben Ohau Range

Climate proxy records from the middle to high latitude Southern Hemisphere indicate that a Lateglacial (15,000-11,500 years ago) climate reversal, approximately coeval with the Antarctic Cold Reversal (ACR), interrupted a warming trend during deglaciation. In New Zealand, some palaeoclimate proxy records indicate a cool episode during the ACR (ca 14,500-12,500 years ago), while others do not express a significant change in climate. Recently published moraine maps and ages present an opportunity to improve the palaeoclimate interpretation through numerical modelling of glaciers. We use a coupled energy-balance and ice-flow model to quantify palaeoclimate from past glacier extent constrained by mapped and dated moraines in the headwaters of Irishman Stream, a high-elevation catchment in the Southern Alps. First, a suite of steady-state model runs is used to identify the temperature and precipitation forcing required to fit the modelled glacier to well-dated Lateglacial moraine crests. Second, time dependent glacier simulations forced by a nearby proxy temperature record derived from chironomids are used to assess the fit with the glacial geomorphic record. Steady-state experiments using an optimal parameter set demonstrate that the conditions under which the 13,000 year old moraine formed were 2.3-3.2 *C colder than present with the range in temperature corresponding to a +/- 20% variance in precipitation relative to the present-day. This reconstructed climate change relative to the present-day corresponds to an equilibrium-line altitude of ca 2000 +/- 40 m above sea level (asl), which is ca 400 m lower than present. Time-dependent simulations of glacier length produce ice advance to within 100 m of the 13,000 year old terminal moraine, indicating that the chironomid-based temperature forcing and moraine record provide consistent information about past climate. Our results, together with other climate proxy reconstructions from pollen records and marine sediment cores, support the notion that temperatures during the ACR in New Zealand were ~2-3 *C cooler than today

The Last Glacial Maximum in the central North Island, New Zealand: palaeoclimate inferences from glacier modelling

Abstract. Quantitative palaeoclimate reconstructions provide data for evaluating the mechanisms of past, natural climate variability. Geometries of former mountain glaciers constrained by moraine mapping afford the opportunity to reconstruct palaeoclimate, due to the close relationship between ice extent and local climate. In this study, we present results from a series of experiments using a 2D coupled energy-balance/ice-flow model that investigate the palaeoclimate significance of Last Glacial Maximum moraines within nine catchments in central North Island, New Zealand. We find that the former ice limits can be simulated when present day temperatures are reduced by between 4 °C and 7 °C, when precipitation remains unchanged from present. The spread in the results between the nine catchments is likely to represent the combination of chronological and model uncertainties. The temperature decrease required to simulate the former glaciers falls in the range of 5.1 °C and 6.3 °C for the majority of catchments targeted, which represents our best estimate of the peak temperature anomaly in central North Island, New Zealand during the Last Glacial Maximum. A decrease in precipitation, as suggested by proxy evidence and climate models, of up to 25 % from present, increases the magnitude of the required temperature changes by up to 0.8 °C. Glacier model experiments using reconstructed topographies that exclude the volume of post-glacial (&lt;15 ka) volcanism, generally increased the magnitude of cooling required to simulate the former ice limits by up to 0.5 °C. Our palaeotemperature estimates expand the spatial coverage of proxy-based quantitative palaeoclimate reconstructions in New Zealand, and are consistent with independent, proximal temperature reconstructions from fossil pollen assemblages, as well as similar glacier modelling reconstructions from central Southern Alps. </jats:p

High-precision 10Be chronology of moraines in the Southern Alps indicates synchronous cooling in Antarctica and New Zealand 42,000 years ago

Millennial-scale temperature variations in Antarctica during the period 80,000 to 18,000 years ago are known to anti-correlate broadly with winter-centric cold–warm episodes revealed in Greenland ice cores. However, the extent to which climate fluctuations in the Southern Hemisphere beat in time with Antarctica, rather than with the Northern Hemisphere, has proved a controversial question. In this study we determine the ages of a prominent sequence of glacial moraines in New Zealand and use the results to assess the phasing of millennial climate change. Forty-four 10Be cosmogenic surface-exposure ages of boulders deposited by the Pukaki glacier in the Southern Alps document four moraine-building events from Marine Isotope Stage 3 (MIS 3) through to the end of the Last Glacial Maximum (∼18,000 years ago; LGM). The earliest moraine-building event is defined by the ages of nine boulders on a belt of moraine that documents the culmination of a glacier advance 42,000 years ago. At the Pukaki locality this advance was of comparable scale to subsequent advances that, from the remaining exposure ages, occurred between 28,000 and 25,000, at 21,000, and at 18,000 years ago. Collectively, all four moraine-building events represent the LGM. The glacier advance 42,000 years ago in the Southern Alps coincides in Antarctica with a cold episode, shown by the isotopic record from the EPICA Dome C ice core, between the prominent A1 and A2 warming events. Therefore, the implication of the Pukaki glacier record is that as early as 42,000 years ago an episode of glacial cold similar to that of the LGM extended in the atmosphere from high on the East Antarctic plateau to at least as far north as the Southern Alps (∼44°S). Such a cold episode is thought to reflect the translation through the atmosphere and/or the ocean of the anti-phased effects of Northern Hemisphere interstadial conditions to the southern half of the Southern Hemisphere. Regardless of the mechanism, any explanation for the cold episode at 42,000 years ago must account for its widespread atmospheric footprint not only in Antarctica but also within the westerly wind belt in southern mid-latitudes

Breast cancer management pathways during the COVID-19 pandemic: outcomes from the UK ‘Alert Level 4’ phase of the B-MaP-C study

Abstract: Background: The B-MaP-C study aimed to determine alterations to breast cancer (BC) management during the peak transmission period of the UK COVID-19 pandemic and the potential impact of these treatment decisions. Methods: This was a national cohort study of patients with early BC undergoing multidisciplinary team (MDT)-guided treatment recommendations during the pandemic, designated ‘standard’ or ‘COVID-altered’, in the preoperative, operative and post-operative setting. Findings: Of 3776 patients (from 64 UK units) in the study, 2246 (59%) had ‘COVID-altered’ management. ‘Bridging’ endocrine therapy was used (n = 951) where theatre capacity was reduced. There was increasing access to COVID-19 low-risk theatres during the study period (59%). In line with national guidance, immediate breast reconstruction was avoided (n = 299). Where adjuvant chemotherapy was omitted (n = 81), the median benefit was only 3% (IQR 2–9%) using ‘NHS Predict’. There was the rapid adoption of new evidence-based hypofractionated radiotherapy (n = 781, from 46 units). Only 14 patients (1%) tested positive for SARS-CoV-2 during their treatment journey. Conclusions: The majority of ‘COVID-altered’ management decisions were largely in line with pre-COVID evidence-based guidelines, implying that breast cancer survival outcomes are unlikely to be negatively impacted by the pandemic. However, in this study, the potential impact of delays to BC presentation or diagnosis remains unknown

A maximum in global glacier extent during MIS 4

The most recent maximum in global ice volume occurred around 23,000 to 19,000 years ago, during Marine Isotope Stage 2 (MIS 2; ∼29-14 ka) according to benthic δ18O and sea level records. However, evidence from cosmogenic surface exposure dating indicates that world-wide many glacier systems of different sizes as well as portions of some ice sheets were more extensive during MIS 4 (∼71-57 ka) and MIS 3 (∼57-29 ka) than they were during MIS 2. This discrepancy between global ice volume and ice extent must be explained in order to understand Earth’s recent paleoclimate history. Here, we review MIS 4 moraine chronologies based on 10Be exposure dating, and we describe additional paleoclimate proxy records that indicate similar magnitudes of cooling during MIS 4 and MIS 2. While certain regions may have benefited from a wetter MIS 4 relative to MIS 2, it is unlikely that precipitation alone can explain more extensive glaciation on a global scale between 71 and 57 ka. Our review supports the hypothesis that the discrepancy between ice volume and ice extent during MIS 4 can be attributed to the growth of the North American ice sheets (and perhaps other northern ice sheets). Glaciers ultimately respond to changes in climate, however, large northern ice sheets also were affected by factors involving topography, isostacy, and glaciologic and mass balance dynamics. Given these feedbacks, the North American ice sheets’ dominant role in global ice volume, sea level, and benthic δ18O signals might therefore result in a skewed picture of global climate. If maximum global ice volume during MIS 2 is mainly a function of North American ice sheet volume and not necessarily directly connected to global temperatures, then other records with extremes during MIS 2, such as dust and CO2, could be primarily reflecting ice volume change

High-latitude warming initiated the onset of the last deglaciation in the tropics

Atmospheric greenhouse gas concentrations are thought to have synchronized global temperatures during Pleistocene glacial–interglacial cycles, yet their impact relative to changes in high-latitude insolation and ice-sheet extent remains poorly constrained. Here, we use tropical glacial fluctuations to assess the timing of low-latitude temperature changes relative to global climate forcings. We report 10Be ages of moraines in tropical East Africa and South America and show that glaciers reached their maxima at ~29 to 20 ka, during the global Last Glacial Maximum. Tropical glacial recession was underway by 20 ka, before the rapid CO2 rise at ~18.2 ka. This “early” tropical warming was influenced by rising high-latitude insolation and coincident ice-sheet recession in both polar regions, which lowered the meridional thermal gradient and reduced tropical heat export to the high latitudes