Stable isotopes and Antarctic moss banks: plants and soil microbes respond to recent warming on the Antarctic Peninsula [abstract only]

The Antarctic Peninsula is one of the most rapidly warming regions on Earth, with air temperature increases of as much as 3°C recorded since the 1950s. However, the longer-term context of this change is limited and existing records, largely relying on ice core data, are not suitably located to be able to trace the spatial signature of change over time. We are working on a project exploiting stable isotope records preserved in moss peat banks spanning 10 degrees of latitude along the Antarctic Peninsula as an archive of late Holocene climate variability. Here we present a unique time series of past moss growth and soil microbial activity that has been produced from a 150 year old moss bank at Lazarev Bay, Alexander Island (69°S), a site at the southern limit of significant plant growth in the Antarctic Peninsula region. These moss banks are ideal archives for palaeoclimate research as they are well-preserved by freezing, generally monospecific, easily dated by radiocarbon techniques, and have sufficiently high accumulation rates to permit decadal resolution. We use accumulation rates, cellulose δ13C and fossil testate amoebae to show that growth rates, assimilation and microbial productivity rose rapidly in the 1960s, consistent with temperature change, although recently may have stalled, concurrent with other evidence. The increase in biological activity is unprecedented in the last 150 years. Along with work completed on Signy Island (60°S), in the South Orkney Islands, in which we used carbon isotope evidence to show recent climate-related enhancement of CO2 assimilation and peat accumulation rates in Antarctica, the observed relationships between moss growth, microbial activity and climate suggests that moss bank records have the potential to test the regional expression of temperature variability shown by instrumental data on the Antarctic Peninsula over centennial to millennial timescales, by providing long-term records of summer growth conditions, complementing the more distant and widely dispersed ice core records. We will conclude by placing the records into the wider context of the latest progress of analysis of moss bank cores obtained along the length of the Antarctic Peninsula and Scotia arc. Royles, J., M. J. Amesbury, P. Convey, H. Griffiths, D. A. Hodgson, M. J. Leng and D. J. Charman (2013). Plants and soil microbes respond to recent warming on the Antarctic Peninsula. Current Biology 23(17): 1702-1706. Royles, J., J. Ogée, L. Wingate, D. A. Hodgson, P. Convey and H. Griffiths (2012). Carbon isotope evidence for recent climate-related enhancement of CO2 assimilation and peat accumulation rates in Antarctica. Global Change Biology 18(10): 3112-3124

Moss stable isotopes (carbon-13, oxygen-18) and testate amoebae reflect environmental inputs and microclimate along a latitudinal gradient on the Antarctic Peninsula.

The stable isotope compositions of moss tissue water (δ(2)H and δ(18)O) and cellulose (δ(13)C and δ(18)O), and testate amoebae populations were sampled from 61 contemporary surface samples along a 600-km latitudinal gradient of the Antarctic Peninsula (AP) to provide a spatial record of environmental change. The isotopic composition of moss tissue water represented an annually integrated precipitation signal with the expected isotopic depletion with increasing latitude. There was a weak, but significant, relationship between cellulose δ(18)O and latitude, with predicted source water inputs isotopically enriched compared to measured precipitation. Cellulose δ(13)C values were dependent on moss species and water content, and may reflect site exposure to strong winds. Testate amoebae assemblages were characterised by low concentrations and taxonomic diversity, with Corythion dubium and Microcorycia radiata types the most cosmopolitan taxa. The similarity between the intra- and inter-site ranges measured in all proxies suggests that microclimate and micro-topographical conditions around the moss surface were important determinants of proxy values. Isotope and testate amoebae analyses have proven value as palaeoclimatic, temporal proxies of climate change, whereas this study demonstrates that variations in isotopic and amoeboid proxies between microsites can be beyond the bounds of the current spatial variability in AP climate.The research was funded by the Natural Environment Research Council Antarctic Funding Initiative grant NE/H014896/ to DJC, PC, DAH and HG. PC, DAH and JR contribute to the BAS ‘Polar Science for Planet Earth’ research programme. Carbon isotope analyses were undertaken by Chris Kendrick at the NERC Isotope Geosciences Laboratory. Sample collection was supported by HMS Protector and HMS Endurance. Thanks to Iain Rudkin and Ashly Fusiarski for fieldwork support, to Adrian Dahood for water sample collection and to Sue Rouillard in the University of Exeter Geography drawing office for Figure 1.This is the final version of the article. It first appeared from Springer via https://doi.org/10.1007/s00442-016-3608-

Can oxygen stable isotopes be used to track precipitation moisture

Variations in the isotopic composition of precipitation are determined by fractionation processes which occur during temperature- and humidity-dependent phase changes associated with evaporation and condensation. Oxygen stable isotope ratios have therefore been frequently used as a source of palaeoclimate data from a variety of proxy archives, which integrate this signal over time. Applications from ombrotrophic peatlands, where the source water used in cellulose synthesis is derived solely from precipitation, have been mostly limited to Northern Hemisphere Sphagnum-dominated bogs, with few in the Southern Hemisphere or in peatlands dominated by vascular plants. New Zealand (NZ) provides an ideal location to undertake empirical research into oxygen isotope fractionation in vascular peatlands because single taxon analysis can be easily carried out, in particular using the preserved root matrix of the restionaceous wire rush (Empodisma spp.) that forms deep Holocene peat deposits throughout the country. Furthermore, large gradients are observed in the mean isotopic composition of precipitation across NZ, caused primarily by the relative influence of different climate modes. Here, we test whether δ18O of Empodisma α-cellulose from ombrotrophic restiad peatlands in NZ can provide a methodology for developing palaeoclimate records of past precipitation δ18O. Surface plant, water and precipitation samples were taken over spatial (six sites spanning >10◦ latitude) and temporal (monthly measurements over one year) gradients. A link between the isotopic composition of root-associated water, the most likely source water for plant growth, and precipitation in both datasets was found. Back-trajectory modelling of precipitation moisture source for rain days prior to sampling showed clear seasonality in the temporal data that was reflected in root-associated water. The link between source water and plant cellulose was less clear, although mechanistic modelling predicted mean cellulose values within published error margins for both datasets. Improved physiological understanding and modelling of δ18O in restiad peatlands should enable use of this approach as a new source of palaeoclimate data to reconstruct changes in past atmospheric circulation

The Oral History Metadata Synchronizer (OHMS) Proposal

Dan Royles proposal for a pedagogical project that connects students to unique primary sources from the past an

Heating up the Holocene

With direct meteorological data on the Antarctic Peninsula only dating back to the 1950s, scientists must search elsewhere for climate change records of the distant past. A series of expeditions to analyse ancient moss are poised to provide a longer-term perspective on the region’s warming pattern

Oral History Training with Dr. Dan Royles

A training conducted by FIU Professor of History Dr. Dan Royles on oral history interviewing best practice. Made in conjunction with the Mellon-funded Community Data Curation project, executed by the Wolfsonian Public Humanities Lab from 2021-2023

Spatially coherent late Holocene Antarctic Peninsula surface air temperature variability

The Antarctic Peninsula experienced a rapid rise in regional temperature during the second half of the 20th century, but the regional pattern of multi-centennial temperature changes and their dynamical drivers remain poorly understood. Here we use proxies of biological productivity in rare, deep moss banks to infer past surface air temperature changes on the Antarctic Peninsula and identify the drivers of these changes. Late Holocene temperatures are broadly consistent between the low-elevation moss bank records and a high-elevation ice core site, and we conclude that variation in the strength of the westerlies, linked to the Southern Annular Mode, is the most likely driver. Our data do not support a hypothesized persistent temperature dipole over the Antarctic Peninsula related to a strong influence of El Nino-Southern Oscillation. Rates of change in biological productivity on the peninsula over the 20th century are unusual in the context of the late Holocene, and further warming will drive rapid future increases in moss growth and microbial populations.Peer reviewe

Plants and soil microbes respond to recent warming on the Antarctic Peninsula

Annual temperatures on the Antarctic Peninsula, one of the most rapidly warming regions on Earth, have risen by up to 0.56°C per decade since the 1950s [1]. Terrestrial and marine organisms have shown changes in populations and distributions over this time [2 and 3], suggesting that the ecology of the Antarctic Peninsula is changing rapidly. However, these biological records are shorter in length than the meteorological data, and observed population changes cannot be securely linked to longer-term trends apparent in paleoclimate data [4]. We developed a unique time series of past moss growth and soil microbial activity from a 150-year-old moss bank at the southern limit of significant plant growth based on accumulation rates, cellulose δ13C, and fossil testate amoebae. We show that growth rates and microbial productivity have risen rapidly since the 1960s, consistent with temperature changes [5], although recently they may have stalled [2]. The recent increase in terrestrial plant growth rates and soil microbial activity are unprecedented in the last 150 years and are consistent with climate change. Future changes in terrestrial biota are likely to track projected temperature increases closely and will fundamentally change the ecology and appearance of the Antarctic Peninsula

Taxonomic Implications of Morphological Complexity Within the Testate Amoeba Genus Corythion from the Antarctic Peninsula

Precise and sufficiently detailed morphological taxonomy is vital in biology, for example in the accurate interpretation of ecological and palaeoecological datasets, especially in polar regions, where biodiversity is poor. Testate amoebae on the Antarctic Peninsula (AP) are well-documented and variations in their population size have recently been interpreted as a proxy for microbial productivity changes in response to recent regional climate change. AP testate amoeba assemblages are dominated by a small number of globally ubiquitous taxa. We examine morphological variation in Corythion spp. across the AP, finding clear evidence supporting the presence of two morphospecies. Corythion constricta (Certes 1889) was identified on the AP for the first time and has potentially been previously misidentified. Furthermore, a southerly trend of decreasing average test size in Corythion dubium (Taránek 1881) along the AP suggests adaptive polymorphism, although the precise drivers of this remain unclear, with analysis hindered by limited environmental data. Further work into morphological variation in Corythion is needed elsewhere, alongside molecular analyses, to evaluate the potential for (pseudo)cryptic diversity within the genus. We advocate a parsimonious taxonomical approach that recognises genetic diversity but also examines and develops accurate morphological divisions and descriptions suitable for light microscopy-based ecological and palaeoecological studies.The research was funded by the NERC Antarctic Funding Initiative Grant NE/H014896 /awarded to DJC, PC and DAH; PC, DAH and JR contribute to the BAS Polar Science for Planet Earth research programme. Sample collection was supported by HMS Protector and HMS Endurance. Thanks to Iain Rudkin and Ashly Fusiarski for fieldwork support, to Ralf Meisterfeld for his help compiling the list of Corythion taxa, to Thomas Ezard for his advice on using mclust, and to Leonardo D. Fernández and Enrique Lara for their help in obtaining rare literature. Finally, we thank three anonymous reviewers for their helpful and insightful comments on an earlier version of this manuscript