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Interactions among multiple stressors, legacies of past perturbations, and the lack of historical information make it difficult to determine the influence of individual anthropogenic impacts on lakes and separate them from natural ecosystem variability. In the present study, we coupled paleolimnological approaches, historical data, and ecological experiments to disentangle the impacts of multiple long-term stressors on lake ecosystem structure and function. We found that the lake structure and function remained resistant to the impacts of catchment deforestation and erosion, and the introduction of several exotic fish species. Changes in ecosystem structure and function were consistent, with nutrient enrichment being the primary driver of change. Significant and sustained changes in the lake diatom community structure (and their nutrient requirements), bacterial community function, and paleolimnological proxies of ecosystem function coincided with nitrogen and phosphorus fertilizers in the catchment. The results highlight that the effects of increased nutrient inputs are much stronger than the influence of other, potentially significant, drivers of ecosystem change, and that the degree of nutrient impact can be underestimated by environmental monitoring due to its diffuse and accumulative nature. Delineating the effects of multiple anthropogenic drivers requires long-term records of both impacts and lake ecosystem change across multiple trophic levels.

Opportunities to study community-level responses to extreme natural pulse disturbances in unaltered ecosystems are rare. Lake sediment records that span thousands of years can contain well-resolved sediment pulses, triggered by earthquakes. These palaeorecords provide a means to study repeated pulse disturbances and processes of resistance (insensitivity to disturbance) and ecological resilience (capacity to regain structure, function and process). In this study, sedimentary DNA was extracted from a sediment core from Lake Paringa (New Zealand) that is situated in a near natural catchment. Metabarcoding and inferred functions were used to assess the lake microbial community over the past 1100 years - a period that included four major earthquakes. Microbial community composition and function differed significantly between highly perturbed (postseismic, ~50 years) phases directly after the earthquakes and more stable (interseismic, ~250 years) phases, indicating a lack of community resistance. Although community structure differed significantly in successive postseismic phases, function did not, suggesting potential functional redundancy. Significant differences in composition and function in successive interseismic phases demonstrate that communities are not resilient to large-scale natural pulse disturbances. The clear difference in structure and function, and high number of indicator taxa (responsible for driving differences in communities between phases) in the fourth interseismic phase probably represents a regime shift, possibly due to the two-fold increase in sediment and terrestrial biospheric organic carbon fluxes recorded following the fourth earthquake. Large pulse disturbances that enhance sediment inputs into lake systems may produce an underappreciated mechanism that destabilises lake ecosystem processes.

Lake sediments are the physical remnants of past allochthonous and autochthonous carbon and mineral inputs and therefore have the potential to illuminate both past terrestrial carbon cycling and wi...

Acid-alkali-acid (AAA) pretreatment is widely used to clean terrestrial plant macrofossil samples for radiocarbon (14C) dating. There is wide variation amongst laboratories in the AAA method details and less rigorous AAA pretreatment is often used on fragile or small samples. Yet there is little evidence as to the efficacy of the different methods and whether the use of less rigorous methods is justified. We investigated four variations of AAA pretreatment: acid only (no alkali wash); room temperature AAA; “standard” AAA at 85°C; and “aggressive” AAA at 85°C with alkali washes repeated until no discoloration was detected. We tested six different terrestrial macrofossils from four different locations and ranging in age from mid-Holocene to the Last Glacial Maximum. Our results demonstrate that while acid only is not always sufficient to remove young material, there is no difference in 14C age of samples pretreated by any of the AAA variants. We also observed mass loss of 85–90% in the standard and aggressive AAA pretreatments, and much more modest mass loss in the room temperature AAA pretreatment. Therefore, we conclude that room temperature AAA pretreatment is optimal to remove contaminating material from fragile terrestrial macrofossils while retaining the majority of the authentic sample material.

Millennial‐scale climate anomalies punctuating the last deglaciation were expressed differently in the Northern and Southern Hemispheres. While changes in oceanic meridional overturning circulation have been invoked to explain these disparities, the nearly synchronous onset of such events requires atmospheric mediation. Yet the extent and structure of atmospheric reorganization on millennial timescales remains unclear. In particular, the role of the Southern Hemisphere westerly winds (SHWW) and associated storm tracks is poorly constrained, largely due to the paucity of accessible archives of wind behavior. Here we present a new paleohydrologic record from a Lake Hayes, New Zealand (45° S) sediment core from ~17‐9 ka. Using two independent proxies for lake hydrology (Ca/Ti in sediments and δD values of aquatic plant biomarkers), we find evidence for a wetter Antarctic Cold Reversal (ACR, 14.7‐13.0 ka) and a drying trend during the Younger Dryas (YD, 12.9‐11.6 ka) and early Holocene (11.7 ka onward in this record). Comparisons of the Lake Hayes record with other Southern Hemisphere sites indicate coherent atmospheric shifts during the ACR and YD, whereby the former is wetter/cooler and the latter is drier/warmer. The wet/cool phase is associated with a northward shift and/or strengthening of the SHWW, whereas the drier/warmer phase indicates weaker mid‐latitude winds. These climatic trends are opposite to the Northern Hemisphere. There is a decoupling of climatic trends between Southern Hemisphere low‐ and mid‐latitude climates in the early Holocene, which could be explained by several mechanisms, such as the retreat of Antarctic sea ice.

Lake sediments accumulate information on biological communities thus acting as natural archives. Traditionally paleolimnology has focussed on fossilized remains of organisms, however, many organisms do not leave fossil evidence, meaning major ecosystem components are missing from environmental reconstructions. Many paleolimnology studies now incorporate molecular methods, including investigating microbial communities using environmental DNA (eDNA), but there is uncertainty about the contribution of living organisms to molecular inventories. In the present study, we obtained DNA and RNA inventories from sediment spanning 700 years to investigate the contribution of past and active communities to the molecular signal from sedimentary archives. Additionally, a droplet digital PCR (ddPCR) targeting the 16S ribosomal RNA (16S rRNA) gene of the photosynthetic cyanobacterial genera Microcystis was used to explore if RNA signals were from legacy RNA. We posit that the RNA signal is a mixture of legacy RNA, dormant cells, living bacteria and modern-day trace level contaminants that were introduced during sampling and preferentially amplified. The presence of legacy RNA was confirmed by the detection of Microcystis in sediments aged to ~200 years ago. Recent comparisons between 16S rRNA gene metabarcoding and traditional paleo proxies showed that past changes in bacterial communities can be reconstructed from sedimentary archives. The recovery of RNA in the present study has provided new insights into the origin of these signals. However, caution is required during analysis and interpretation of 16S rRNA gene metabarcoding data especially in recent sediments were there are potentially active bacteria.

Freshwater eels are ecologically, and culturally important worldwide. The New Zealand long-finned eel (Anguilla dieffenbachii) and short-finned eel (Anguilla australis) are apex predators, playing an important role in ecosystem functioning of rivers and lakes. Recently, there has been a national decline in their populations due to habitat destruction and commercial harvest. The emergence of targeted environmental DNA detection methodologies provides an opportunity to enhance information about their past and present distributions. In this study we successfully developed species-specific droplet digital Polymerase Chain Reaction (ddPCR) assays to detect A. dieffenbachii and A. australis DNA in water and sediment samples. Assays utilized primers and probes designed for regions of the mitochondrial cytochrome b and 16S ribosomal RNA genes in A. dieffenbachii and A. australis, respectively. River water samples (n = 27) were analyzed using metabarcoding of fish taxa and were compared with the ddPCR assays. The presence of A. dieffenbachii and A. australis DNA was detected in a greater number of water samples using ddPCR in comparison to metabarcoding. There was a strong and positive correlation between gene copies (ddPCR analyses) and relative eel sequence reads (metabarcoding analyses) when compared to eel biomass. These ddPCR assays provide a new method for assessing spatial distributions of A. dieffenbachii and A. australis in a range of environments and sample types.

The frequency and intensity of cyanobacterial blooms is increasing worldwide. Multiple factors are implicated, most of which are anthropogenic. New Zealand provides a useful location to study the impacts of human settlement on lake ecosystems. The first humans (Polynesians) arrived about 750 years ago. Following their settlement, there were marked landscape modifications which intensified after European settlement about 150 years ago. The aims of this study were to reconstruct cyanobacterial communities in six lakes over the last 1000 years and explore key drivers of change. Cyanobacterial environmental DNA was extracted from sediment cores and analysed using metabarcoding and droplet digital PCR. Cyanobacteria, including potentially toxic or bloom forming species, were already present in these lakes prior to human arrival, however their overall abundance was low. Total cyanobacteria abundance and richness increased in all lakes after European settlement but was very pronounced in four lakes, where bloom-forming taxa became dominant. These shifts occurred concomitant with land-use change. The catchment of one deteriorated lake is only moderately modified, thus the introduction of non-native fish is posited as the key factor driving this change. The paleolimnological approach used in this study has enabled new insights into timing and potential causes of changes in cyanobacterial communities.

The Holocene thermal maximum (HTM) is a spatio-temporally variable period of generally warmer conditions during the early and middle Holocene that is often used as an analogue for future climate change. Global scale climate reconstructions and models tend to smooth out the variations and complexity of the HTM and inconsistencies between reconstructions from different locations and proxies are often attributed to bias arising from different locations or proxies. We use these differences as a source of information about seasonality and precipitation during the Holocene in a multi-proxy investigation of the sediments of Lake Pupuke, northern New Zealand. The sediments, spanning the last 16 kyr, were analysed for pollen, from which mean annual air temperatures (MAAT) and effective precipitation were estimated, and chironomids, from which summer air temperature (SmT) was estimated. We found no evidence for an HTM in the MAAT reconstruction, questioning the validity of treating the early-to-mid Holocene as an analogue for future climate change in northern New Zealand. SmT increases between 10 and 3 cal kyr BP, correlating strongly with integrated local summer insolation. Early-Holocene low seasonality (from 12 to 9.3 cal kyr BP) was likely driven by low local summer insolation intensity. An early-to-mid-Holocene wet period (9.6–7.5 cal kyr BP) corresponds to relatively high southern westerly wind (SWW) strength. Mid-to-late-Holocene summers following the wet period were hot and dry, especially 4.0–2.4 cal kyr BP, allowing the tall conifer, kauri (Agathis australis) to expand throughout northern New Zealand. Low effective precipitation at this time is consistent with increased evapotranspiration due to higher SmT, although reduced precipitation due to southward displaced SWW or increased El Nino frequency may also have contributed.

Opportunities to study and understand community level responses to extreme natural pulse disturbances in unaltered ecosystems are rare. Lake sediment records that span thousands of years can contain well resolved sediment pulses, triggered by earthquakes. These paleo-records provide a means to study repeated pulse disturbance and the processes of resistance (insensitivity to disturbance) and ecological resilience (capacity to regain structure, function and process). In this study, DNA preserved in lake sediment layers was extracted from a sediment core from a lake in a near-natural catchment. Metabarcoding and inferred functions were used to assess the lake microbial community over the past 1,100 years – a period that included four major earthquakes. Microbial community composition and function differed significantly between highly perturbed (postseismic, c. 50 yrs) phases directly after the earthquakes and more stable (interseismic, c. 260 yr) phases, indicating a lack of community resistance to natural pulse disturbances. A decoupling between community structure and function in successive postseismic phases suggest potential functional redundancy in the community. Significant differences in composition and function in successive interseismic phases demonstrates the communities are not resilient to large scale natural pulse disturbances. The clear difference in structure and function, and high number of indicator taxa in the fourth interseismic phase likely represents a regime shift, possibly due to the two-fold increase in sediment and terrestrial biospheric organic carbon fluxes recorded following the fourth earthquake. Large pulse disturbances that enhance sediment inputs into lake systems may produce an underappreciated mechanism that destabilises lake ecosystem processes.

A continuous record of environmental history is stored in lake sediments providing an avenue to explore current and historical lake communities. Traditionally paleolimnological methods have focussed on macroscopic indicators (e.g. pollen, chronomids, diatoms) to investigate environmental changes but the application of environmental DNA techniques has enabled the investigation of microbial communities and other soft bodied organisms through time. The ‘Our lakes’ health; past, present, future (Lakes380)’ project aims to combined traditional and molecular methods to explore shifts in biological communities over the last 1,000 years (pre-human arrival in New Zealand). Sediments cores have been collected from a wide diversity of lakes across New Zealand and 16S rRNA gene metabarcoding approaches of both DNA and RNA applied to reveal how microbial community changes across time and especially in response to the arrival of humans and associated changes to the landscape and lake environments. We further investigate the changes in inferred metabolic potential of the microbial communities as the taxonomic composition of the lake differs over time. Finally, we combine these novel molecular methods with hyperspectral scanning and pollen data to increase the knowledge of changes in lake communities and identifying the timing of changes in lake health. The combination of methodologies provides a greater understanding of the environmental history of lake systems and will help to inform management decisions relating to the restoration and protection of lake health.

Phytoplankton (including cyanobacteria) are a natural component of lake ecosystems and are the base of many food webs. However, changes in the lake catchment, the lake itself and the wider environment (e.g., climate change) can alter the composition of phytoplankton communities. Of recent concern is the increase in the abundance of cyanobacteria and the formation of blooms in many of New Zealand’s low-land lakes (>30% of those that are monitored). Because regular monitoring data does not stretch back more than 10-30 years and many lakes are not regularly monitored, it is difficult to ascertain whether the intensity of present-day blooms are a new phenomenon or are part of a pre-existing cycle. The pigments produced by cyanobacteria (and other phytoplankton) are deposited in lake sediment and can be extracted from sediment cores and surface sediment samples. Analysis of these pigments by high-performance liquid chromatography has allowed us to reconstruct the historical phytoplankton community from nine New Zealand lakes and to track the emergence of cyanobacteria in impacted lakes. We will present data on the performance of different cyanobacteria pigment indicators and several case studies to demonstrate how fossilised pigment data can be used to understand shifts in lake phytoplankton communities.

Anthropogenic nutrient enrichment, hydrological modifications, and introduced species are contributing to an increase in the frequency and intensity of cyanobacterial blooms. This study aimed to document the evolution of cyanobacterial assemblages over time and explore the drivers of cyanobacterial blooms. Environmental DNA was extracted from sediment cores dating back approximately 1,000-years collected from six New Zealand lakes (Rotoehu, Pounui, Wairarapa, Paringa, Johnson, Hayes). Samples were analysed using cyanobacterial 16S rRNA metabarcoding and droplet digital PCR. Picocyanobacteria had the highest relative abundance. Marked shifts in species composition were observed over time but species varied between lakes. Marked shifts in total abundance (from ddPCR data) were observed through time in all lakes, and the metabarcoding data revealed these abundances to be bloom-forming taxa only in impacted lakes. Historical cyanobacterial communities seemed to be mostly influenced by anthropogenic activities and the geographic location of the lakes. Comparison with other paleolimnological proxies suggests land-use and non-native fish as key drivers in species and abundance shifts. Sedimentary environmental DNA analysis can complement traditional paleo-approaches, and provide novel information on microbial communities, and new insights into causes and consequences of cyanobacterial blooms.

Lake sediments are natural archives that accumulate information about biological communities and their surrounding catchments. Paleolimnology has traditionally focussed on identifying fossilized organisms to reconstruct past environments. In the last decade, the application of molecular methodologies has increased in paleolimnological studies, but further studies investigating factors such as sample heterogeneity and DNA degradation are required. Here we investigated bacterial community heterogeneity (16S rRNA metabarcoding) within depth slices. Sediment cores were collected from three lakes with differing sediment compositions. Samples were collected from a variety of depths (1-cm width) which represent a period of time of approximately 1,200 years. Triplicate samples were collected from each slice and bacterial 16S rRNA metabarcoding was undertaken on each sample. Rarefaction curves showed that except for the deepest (oldest) slices, the combination of three replicate samples were insufficient to characterise the entire bacterial diversity. However, shared Amplicon Sequence Variants (ASVs) accounted for the majority of the reads in each slice (max. shared proportional read abundance 96%, 86%, 65% in the three lakes). Within slice similarity was higher than between slice similarity. No general trend was observed in variability among replicates with depth amongst the lakes. In one core. there was a higher community dissimilarity in older sediment, which may be due to laminae not being horizontal. These results highlight the fact that microbial communities can be differentiated with depth however it is critical to interpret these results in the context of the stratigraphic data of the core.

Lake surface sediments are dominated by microorganisms that play significant roles in biogeochemical cycling within lakes. There is limited knowledge on the relative importance of local environmental factors and altitude on bacterial and microeukaryotic community richness and composition in lake sediments. In the present study, surface sediment samples were collected from 40 lakes along an altitude gradient (2–1215 m). Microbial communities were characterized using 16S (bacteria) and 18S (microeukaryotes) rRNA gene metabarcoding. Bacterial and microeukaryotic richness were not correlated with altitude but instead to environmental variables (e.g. area of water in the catchment (bacteria: R = −0.43). For both bacteria and microeukaryotes, dissimilarity in the community structure had a higher correlation to combined environmental variables (without altitude) (bacteria: R = 0.53; microeukaryotes: R = 0.55) than altitude alone (bacteria: R = 0.34; microeukaryotes: R = 0.47). Sediment sulfur and productive grassland were important variables in determining the relative abundance of sulfate reducing bacteria. Nitrospira, was positively related to altitude but negatively to water column total organic carbon and the proportion of productive grassland in the catchment. Little overlap in amplicon sequence variants was shown amongst lakes. This has important considerations for management decisions, suggesting that to protect biodiversity, conservation of numerous lakes and lake types is required.

Annually resolved (varved) lake sequences are important palaeoenvironmental archives as they offer a direct incremental dating technique for high-frequency reconstruction of environmental and climate change. Despite the importance of these records, establishing a robust chronology and quantifying its precision and accuracy (estimations of error) remains an essential but challenging component of their development. We outline an approach for building reliable independent chronologies, testing the accuracy of layer counts and integrating all chronological uncertainties to provide quantitative age and error estimates for varved lake sequences. The approach incorporates (1) layer counts and estimates of counting precision; (2) radiometric and biostratigrapic dating techniques to derive independent chronology; and (3) the application of Bayesian age modelling to produce an integrated age model. This approach is applied to a case study of an annually resolved sediment record from Lake Ohau, New Zealand. The most robust age model provides an average error of 72 years across the whole depth range. This represents a fractional uncertainty of ∼5%, higher than the

The Last Glacial-Interglacial Transition (LGIT) was a dynamic stage of Earth's history, and the difficulty of reconstructing this complex interval may be compounded by divergent proxy records, often collected from the same archive. To overcome this obstacle, we exploit the contrasting biological preferences of chironomids to both summer temperature and degree days (positive) and pollen to both the length of the growing season (positive) and winter duration (negative), recorded by a small lake in the central North Island of New Zealand. The climate proxy records are anchored to shifting zonal boundaries (e.g., southern westerly wind belt) via the hydrogen isotope ratios of leaf wax n-alkanes (δDwax). These results enable us to interrogate the structure of the LGIT and address two fundamental questions: 1) Is there evidence for Holocene-like temperatures during the early deglacial? and 2) Were early Holocene summers cool? Lake sediment δDwax values indicate a poleward retreat of the westerlies around 18,000 calibrated years before present (cal kyr BP), signalling the onset of climate amelioration for the region. Remarkably, the independently derived summer and mean annual temperature reconstructions are anti-phased. Chironomid-inferred summer temperatures surpass modern values by 17.5 cal kyr BP, whereas pollen-inferred mean annual temperatures remain supressed. Summers cool from 17.5 to 11 cal kyr BP, when they reach a minimum for the record, while winter and mean annual temperatures simultaneously warm to a maximum. The chironomid record generally traces regional insolation, although an Antarctic template imprints on this trend with declining summer temperatures during the Antarctic Cold Reversal (ACR) and warming during the Younger Dryas (YD). Forest development during the early LGIT, on the other hand, is supressed by cool, dry winters, punctuated by severe frosts, despite being set against a backdrop of overall warming; the successional pattern is best explained by a latitudinal retreat of the westerlies. Our findings underscore the complementarity of multiple bioproxy responses and reveal the importance of seasonal heat and energy distribution during the LGIT.

Discovery and investigation of millennial-scale geological records of past large earthquakes improve understanding of earthquake frequency, recurrence behaviour, and likelihood of future rupture of major active faults. Here we present a ∼2000 year-long, seven-event earthquake record from John O'Groats wetland adjacent to the Alpine fault in New Zealand, one of the most active strike-slip faults in the world. We linked this record with the 7000 year-long, 22-event earthquake record from Hokuri Creek (20 km along strike to the north) to refine estimates of earthquake frequency and recurrence behaviour for the South Westland section of the plate boundary fault. Eight cores from John O'Groats wetland revealed a sequence that alternated between organic-dominated and clastic-dominated sediment packages. Transitions from a thick organic unit to a thick clastic unit that were sharp, involved a significant change in depositional environment, and were basin-wide, were interpreted as evidence of past surface-rupturing earthquakes. Radiocarbon dates of short-lived organic fractions either side of these transitions were modelled to provide estimates for earthquake ages. Of the seven events recognised at the John O'Groats site, three post-date the most recent event at Hokuri Creek, two match events at Hokuri Creek, and two events at John O'Groats occurred in a long interval during which the Hokuri Creek site may not have been recording earthquakes clearly. The preferred John O'Groats–Hokuri Creek earthquake record consists of 27 events since ∼6000 BC for which we calculate a mean recurrence interval of 291 ± 23 years , shorter than previously estimated for the South Westland section of the fault and shorter than the current interseismic period. The revised 50-year conditional probability of a surface-rupturing earthquake on this fault section is 29%. The coefficient of variation is estimated at 0.41. We suggest the low recurrence variability is likely to be a feature of other strike-slip plate boundary faults similar to the Alpine fault.

Identifying arboriculture and agroforestry in Polynesian Societies has usually relied heavily upon the ethnographic record in the absence of direct archaeological evidence. In this paper we outline a multi-proxy research design, including ethnography, palynology, anthracology, archaeology and a high precision chronology to evaluate arboriculture and agroforestry as components of Moriori subsistence practices before the arrival of Europeans in 1791. The colonisers of Rekohu brought with them a mainland New Zealand endemic tree, Corynocarpus laevigatus, and the technology to propagate the tree in a less than ideal climate and to process its drupe into a storable source of carbohydrate in what was a difficult environment for Polynesian cultivation practices. We also present a conceptual model of forest change due to Moriori fuel selection practices which suggests that Moriori were actively managing these forest spaces for food, fuel, medicine, construction material and as a habitation space, therefore making agroforestry an important component of Moriori subsistence.

Branched glycerol dialkyl glycerol tetraethers (brGDGTs) were abundant in surface sediments of freshwater lakes and in catchment soils at altitudes from 10 to 2020m in New Zealand. Significant differences in brGDGT compositions between lake sediments and soils indicate sources from separate microbial habitats. An expanded modern calibration dataset comprising 33 lakes has enabled a revised calibration function for determining past mean annual air temperature (MAT) from brGDGTs in New Zealand lake sediments: MAT (degrees C) = -31.664 x MBTm + 16.252 (n = 30). The function uses a modified methylation index of branched tetraethers (MBTm) that incorporates brGDGT III in the numerator to overcome the lower correlation found between our larger dataset and the unmodified MBT which had been used for previous calibrations. Calibrations combining the cyclization index of branched tetraethers (CBT) and the MBTm or using only certain brGDGTs are possible but have limitations. The revised function shows slightly higher correlation with MAT (R-2 = 0.75) than previous calibrations, which were based on nine sites. The refined calibration function is applied to a similar to 16 000-year lake sediment sequence from northern South Island, New Zealand, and yields temperature reconstructions that are consistent with independently derived climate trends from the same sequence. Copyright (C) 2016 John Wiley & Sons, Ltd.

Subantarctic islands are located at a critical latitude for reconstructing past changes in ocean-atmosphere interactions. Currently, there is a lack of high-resolution records from the Pacific sector of the Southern Ocean that can be used to reconstruct climate since the Last Glacial Maximum (LGM). Here, we present a reconstruction of environmental change from a fjord ingression basin at New Zealand’s subantarctic Auckland Islands (50.5°S) over the last ∼19 ka cal BP. Using sedimentological and geochemical analysis of cores collected along a depth transect in Norman Inlet we find evidence for four different stages of environmental history: deglacial, lacustrine, marine transgression, and marine. Glaciers retreated from their maximum extent before 19.4 ka cal BP during a period of ice retreat that appears synchronous across the Pacific basin, likely due to southward migration of the Subtropical Front. However, in contrast to other glaciated regions, we see no evidence for ice re-advance, and a proglacial lake was present in the basin until 15.7 ka cal BP. Following deglaciation, organic-rich sedimentation dominated the lacustrine environment until post-glacial sea-level rise flooded the depositional basin at 8.8 ka cal BP. Deposition of organic-rich sediment continued during the Antarctic Cold Reversal and we find no evidence for a glacial re-advance. Mixing of terrestrial and marine organic matter during the marine transgression (8.8–6.7 ka cal BP) indicates significant erosion and re-working of sediment in the catchment as seawater overtopped the sill. Modern fjord circulation commenced ∼6.7 ka cal BP when sea level reached its maximum in the early Holocene. This well-dated, high-resolution record constrains the timing of deglaciation, sea-level rise, and subantarctic environmental change following the LGM that expands our understanding of the key drives of climate change in the middle to high southern latitudes.

The occurrence of terrestrial palynomorphs in Quaternary marine sedimentary sequences allows for direct land–sea correlations and provides a means for transferring Marine Isotope Stage chronologies to terrestrial records that extend beyond the range of radiocarbon dating. Both of these important applications require an implicit assumption that the lag between pollen release and final deposition on the seafloor – here referred to as source-to-sink residence time – is negligible in relation to the chronological resolution of the sedimentary sequence. Most studies implicitly assume zero lag, and where studies do take palynomorph residence time into account, its magnitude is rarely quantified. In Westland, New Zealand, fluvial transport is the main source of delivery of terrestrial pollen offshore to the adjacent East Tasman Sea. We radiocarbon-dated organic matter carried and deposited by contemporary Westland rivers that drain catchments with varying degrees of disturbance. The ages obtained ranged widely from essentially modern (i.e., − 57 ± 22 cal yr BP) to 3583 ± 188 cal yr BP, suggesting that precisely constraining the residence time in this region is unlikely to be achieved. We also compared the timing of four palynomorph events characterising Westland's late Pleistocene, along with the well-dated Kawakawa/Oruanui Tephra (KOT), between marine core MD06-2991 and four terrestrial records from Westland. Critically, all palynomorph events and the KOT are chronologically indistinguishable with respect to the independently dated marine and terrestrial records, supporting the general principle of transferring the marine chronology onto the terrestrial records in this setting. In other regions, particularly those lacking the high soil production and erosion rates that characterise Westland, we suggest that similar tests of marine residence time should be conducted before assumptions of zero or negligible lag are invoked.

We present a comprehensive 10Be chronology for Holocene moraines in the Lago Argentino basin, on the east side of the South Patagonian Icefield. We focus on three different areas, where prior studies show ample glacier moraine records exist because they were formed by outlet glaciers sensitive to climate change. The 10Be dated records are from the Lago Pearson, Herminita Península-Brazo Upsala, and Lago Frías areas, which span a distance of almost 100 km adjacent to the modern Icefield. New 10Be ages show that expanded glaciers and moraine building events occurred at least at 6120 ± 390 (n = 13), 4450 ± 220 (n = 7), 1450 or 1410 ± 110 (n = 18), 360 ± 30 (n = 5), and 240 ± 20 (n = 8) years ago. Furthermore, other less well-dated glacier expansions of the Upsala Glacier occurred between ~1400 and ∼1000 and ∼2300 and ∼2000 years ago. The most extensive glaciers occurred over the interval from ∼6100 to ∼4500 years ago, and their margins over the last ∼600 years were well within and lower than those in the middle Holocene. The 10Be ages agree with 14C-limiting data for the glacier histories in this area. We then link southern South American, adjacent South Atlantic, and other Southern Hemisphere records to elucidate broader regional patterns of climate and their possible causes. In the early Holocene, a far southward position of the westerly winds fostered warmth, small Patagonian glaciers, and reduced sea ice coverage over the South Atlantic. Although we infer a pronounced southward displacement of the westerlies during the early Holocene, these conditions did not occur throughout the southern mid-high latitudes, an important exception being over the southwest Pacific sector. Subsequently, a northward locus and/or expansion of the winds over the Patagonia-South Atlantic sector promoted the largest glaciers between ∼6100 and ∼4500 years ago and greatest sea ice coverage. Over the last few millennia, the South Patagonian Icefield has experienced successive century-scale advances superimposed on a long-term net decrease in size. Our findings indicate that glaciers and sea ice in the Patagonian-South Atlantic sector of the Southern Hemisphere did not achieve their largest Holocene extents over the last millennium. We conclude that a pattern of more extensive Holocene ice prior to the last millennium is characteristic of the Southern Hemisphere middle latitudes, which differs from the glacier history traditionally thought for the Northern Hemisphere. Fil: Kaplan, Michael. Lamont Doherty Earth Observatory; Estados Unidos Fil: Schaefer, Joerg. Lamont Doherty Earth Observatory; Estados Unidos Fil: STRELIN, Jorge Adrián. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: Denton, George. Lamont Doherty Earth Observatory; Estados Unidos. University Of Maine; Estados Unidos Fil: Anderson, R. F.. University Of Maine; Estados Unidos. Lamont Doherty Earth Observatory; Estados Unidos Fil: Vandergoes, M.. GNS Science; Estados Unidos Fil: Finkel, R.. California State University; Estados Unidos Fil: Schwartz, Roseanne. Lamont Doherty Earth Observatory; Estados Unidos Fil: Travis, S.. General Communication Inc.; Estados Unidos Fil: Garcia, J. L.. University Of Maine; Estados Unidos. Pontificia Universidad Católica de Chile; Chile Fil: Martini, Mateo Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: Nielsen, S. H. H.. Kenex Ltd.; Nueva Zelanda

The Wairarapa Valley possesses strong ecological, economic and cultural heritage in New Zealand; however, it has also been extensively modified by human land-use practices. Despite the value of the Wairarapa Valley's natural heritage, little has been done to quantify anthropogenic impacts. We integrate ‘paleo’ and modern analyses of sediment deposition and assess major changes in Lake Wairarapa's depositional environment. Accumulation rates and grain-size statistics indicate that a major natural disturbance occurred at 2.5 cal kyr BP, whereas charcoal counts register the regional impact of Polynesian forest clearing and GIS analysis quantifies the reduction of Lake Wairarapa's surface area following the Lower Wairarapa Valley Development Scheme. Critically, areas with historically slow accumulation rates are now depositional zones and areas with historically high accumulation rates are now losing sediment. This study illustrates how recent modifications to New Zealand lakes can be set in a long-te...

Determining the earthquake segmentation of plate-boundary transform faults remains a scientific challenge because paleoseismic data sets rarely resolve the end points of past ruptures. In this study, we test whether lacustrine paleoseismology can be used to assess rupture end points and the earthquake segmentation of the Alpine fault, one of the longest and fastest-slipping plate-boundary transform faults on Earth. Sediment cores from Lake Ellery record eight episodes of high-intensity shaking (modified Mercalli intensity [MM] IX) from Alpine fault earthquakes as event sequences of a turbidite produced by coseismic subaqueous mass wasting, overlain by deposits representing sediment flux from co- and postseismic landsliding in the fluvial catchment. Age-depth modeling constrains the timing of shaking events at a decadal resolution, facilitating correlation with two previously published lake records to reconstruct the spatial distribution of MM IX shaking along ~150 km of the Alpine fault. When resolved with existing on- and near-fault paleoseismic records, the lake data set demonstrates that independent ruptures of the South Westland and Central segments occurred in A.D. 845–775 and A.D. 739–646, and A.D. 646–592 and A.D. 416–370, respectively. Lakes adjacent to the Alpine fault provide paleoseismic records with sufficient spatial and temporal resolution to define along-strike differences in the pattern of rupture capable of distinguishing rupture termination at a geometric segment boundary. This multilake study suggests that locating the end points of ruptures using lacustrine paleoseismology will be most applicable in midlatitude convergent plate-boundary settings where along-strike topography and Quaternary glaciation have resulted in the widespread distribution of suitable lakes.

We present a 16 000-year vegetation and climate reconstruction from pollen and plant macrofossil records obtained at a small alpine lake in South Island, New Zealand (41°S). The expansion of lowland forest taxa suggests a lifting of the altitudinal forest limits because of a warming pulse between 13 and 10k cal a BP and between 7 and 6k cal a BP, while their decline relative to upland forest taxa indicates cooling phases between 10 and 7k cal a BP and over the last 3000 years. The modern treeline was first established locally by 9.7k cal a BP. Forest persisted at the site until 3k cal a BP then disappeared from the record. Close correspondence between the temperature trends inferred from the pollen and macrofossil records and proxies from Antarctica and the Southern Ocean suggests a strong teleconnection between New Zealand and the Southern Hemisphere high-latitudes between 15 and 6k cal a BP. We note that the breakdown of this coupling, a cooling trend in Adelaide Tarn and the local disappearance of beech forest after 3k cal a BP occur during a period of increased frequency of El Nino events, suggesting an enhanced teleconnection with the low-latitudes during the late Holocene.

Annually laminated sediments collected from Lake Ohau, New Zealand offer an opportunity to generate a high-resolution paleoclimate record for the Southern Hemisphere mid-latitudes. Correlation between regional precipitation and synoptic climate indices like the Southern Annular Mode, paired with a correlation between Ohau catchment precipitation, lake inflow and suspended sediment yield suggest that the Lake Ohau varves are a potentially powerful tool for estimating the amplitude, timing and interdependence of different climate modes operating in the Southern Hemisphere mid-latitudes over time. A robust chronology and sound climate-proxy model are fundamental requirements for all high-resolution paleoenvironmental records. Here we present a chronology derived from layer counts, and 137Cs and 210Pb ages for the top 60 cm of sediments from the distal basin of Lake Ohau that confirm the varved natured of the sedimentary sequence. Sedimentary facies of different varve motifs are used to develop a hydroclimate-proxy model which links stratigraphy to seasonal hydrology. To establish this relationship we use a model accuracy statistic, which shows a quantitative difference between the annual hydrographs associated with each of three primary varve motifs. Distribution of above average inflow events points to summer and autumn hydrologic regimes as the primary control on the deposition of different motifs. This relationship between varve characteristics and hydrology will serve as a tool to reconstruct lake inflow, and by extension precipitation, on an annual basis throughout the late-Holocene for the South Island of New Zealand.

The Southern Alps are an ideal locality for studying patterns of isotopic fractionation associated with orographic precipitation. We have evaluated whether altitudinal change is reflected in the stable hydrogen isotopic composition (δ 2 H) of stream water, plant stem water and leaf wax lipids ( n -alkanes) from living plants and soils, as well as in soil temperature. Samples were collected along an altitudinal transect from the windward side of the Southern Alps to Lake Hawea in the rain shadow. The results indicate that δ 2 H values of stem water overlap with stream water, demonstrating a gradual decrease with elevation that complied with modeled Rayleigh distillation, reflecting an isotopic lapse rate of −18.0 (± 1.1, 1 σ )‰/km. Leaf and soil n -alkanes shared similar δ 2 H values and were 2 H depleted relative to stem/stream waters. The values for soil n -alkanes indicated an isotopic lapse rate of −21.8 (± 2.0, 1 σ )‰/km, consistent with precipitation data and long term observations. MBT/CBT derived soil temperature values based on the relative distribution of microbial tetraether lipids were similar to midsummer temperature observations, displaying an elevational decrease rate of −5.6 (± 1.5, 1 σ ) °C/km, consistent with regional and global observations. The results indicate that sedimentary lipid δ 2 H and microbial tetraether temperature estimates captured altitudinal trends in the isotopic composition of precipitation and mean temperature and further support their application in the reconstruction of past climate and surface uplift histories. However, notable differences in isotopic composition and temperature estimates between in situ soils and those with downslope transport of material emphasize the importance of facies analysis when interpreting past systems.

Calculation of surface exposure ages, using in situ cosmogenic nuclides, requires accurate knowledge of local production rates. Here, we report the first attempt to calibrate cosmogenic 3He production in the south-west Pacific region. We present a new radiocarbon chronology that precisely dates the emplacement of the Murimotu Formation, a large debris avalanche deposit in central North Island, New Zealand (ca. 830 m asl; 39°S), which occurred 10.4–10.6 cal ka BP. Measurements of cosmogenic 3He in pyroxene separated from large andesitic blocks exposed during this event yield a sea-level high-latitude production rate of 120 ± 12 atoms g−1 a−1 (‘Lm’ scaling). This is consistent with a recent global compilation, comprised predominantly of calibration sites located in the Northern Hemisphere. Thus, we conclude that the globally compiled cosmogenic 3He production rate is valid in the south-west Pacific. Using independent, proximal calibrations of cosmogenic isotopes 10Be and 14C from quartz in New Zealand, we derive cosmogenic 3He/10Be and 3He/14C production ratios of 32.2 ± 3.2 and 10.6 ± 1.6, respectively.