Seismic stratigraphy of the Blue Hole (Lighthouse Reef, Belize), a late Holocene climate and storm archive

Five seismic units may be identified in the similar to 8 m thick Holocene sediment package at the bottom of the Blue Hole, a 120 m deep sinkhole located in the atoll lagoon of Lighthouse Reef, Belize. These units may be correlated with the succession of an existing 5.85-m-long sediment core that reaches back to 1385 kyrs BP. The identification of seismic units is based on the fact that uniform, fine-grained background sediments show weak reflections while alternating background and coarser-grained event (storm) beds exhibit strong reflections in the seismic profiles. The main source of sediments is the marginal atoll reef and adjacent lagoon area to the east and north. Northeasterly winds and storms transport sediment into the Blue Hole, as seen in the eastward increase in sediment thickness, i.e., the eastward shallowing of the Blue Hole. Previous assumptions of much thicker Holocene sediment packages in the Blue Hole could not be confirmed. So far, close to 6-m-long cores were retrieved from the Blue Hole but the base of the sedimentary succession remains to be recovered. The nature of the basal sediments is unknown but mid-Holocene and possibly older, Pleistocene sinkhole deposits can be expected. The number of event beds identified in the Blue Hole (n = 37) during a 1.385 kyr-long period and the number of cyclones listed in historical databases suggest that only strong hurricanes (categories 4 and 5) left event beds in the Blue Hole sedimentary succession. Storm beds are numerous during 13-0.9 kyrs BP and 0.8-0.5 kyrs BP.

Water versus ice: The competing roles of modern climate and Pleistocene glacial erosion in the Central Alps of Switzerland

Recent studies have identified relationships between landscape form, erosion and climate in regions of landscape rejuvenation, associated with increased denudation. Most of these landscapes are located in non-glaciated mountain ranges and are characterized by transient geomorphic features. The landscapes of the Swiss Alps are likewise in a transient geomorphic state as seen by multiple knickzones. In this mountain belt, the transient state has been related to erosional effects during the Late Glacial Maximum (LGM). Here, we focus on the catchment scale and categorize hillslopes based on erosional mechanisms, landscape form and landcover. We then explore relationships of these variables to precipitation and extent of LGM glaciers to disentangle modern versus palaeo controls on the modern shape of the Alpine landscape. We find that in grasslands, the downslope flux of material mainly involves unconsolidated material through hillslope creep, testifying a transport-limited erosional regime. Alternatively, strength-limited hillslopes, where erosion is driven by bedrock failure, are covered by forests and/or expose bedrock, and they display oversteepened hillslopes and channels. There, hillslope gradients and relief are more closely correlated with LGM ice occurrence than with precipitation or the erodibility of the underlying bedrock. We relate the spatial occurrence of the transport- and strength-limited process domains to the erosive effects of LGM glaciers. In particular, strength-limited, rock dominated basins are situated above the equilibrium line altitude (ELA) of the LGM, reflecting the ability of glaciers to scour the landscape beyond threshold slope conditions. In contrast, transport-limited, soil-mantled landscapes are common below the ELA. Hillslopes covered by forests occupy the elevations around the ELA and are constrained by the tree line. We conclude that the current erosional forces at work in the Central Alps are still responding to LGM glaciation, and that the modern climate has not yet impacted on the modern landscape.

Site and Age Condition the Growth Responses to Climate and Drought of Relict Pinus nigra subsp. salzmannii Populations in Southern Spain

To assess if tree age may modulate the main climatic drivers of radial growth, two relict Pinus nigra subsp. salzmannii populations (Maria, most xeric site; Magina, least xeric site) were sampled in southern Spain near the limits of the species range. Tree-ring width residual chronologies for two age groups (mature trees, age <= 100 years (minimum 40 years); old trees, age > 100 years) were built to evaluate their responses to climate by relating them to monthly precipitation and temperature and a drought index (DRI) using correlation and response functions. We found that drought is the main driver of growth of relict P. nigra populations, but differences between sites and age classes were also observed. First, growth in the most xeric site depends on the drought severity during the previous autumn and the spring of the year of tree-ring formation, whereas in the relatively more mesic site growth is mainly enhanced by warm and wet conditions in spring. Second, growth of mature trees responded more to drought severity than that of old trees. Our findings indicate that drought severity will mainly affect growth of relict P. nigra populations dominated by mature trees in xeric sites. This conclusion may also apply to similar mountain Mediterranean conifer relicts.

Climate and soil attributes determine plant species turnover in global drylands

Aim Geographical, climatic and soil factors are major drivers of plant beta diversity, but their importance for dryland plant communities is poorly known. The aim of this study was to: (1) characterize patterns of beta diversity in global drylands; (2) detect common environmental drivers of beta diversity; and (3) test for thresholds in environmental conditions driving potential shifts in plant species composition. Location Global. Methods Beta diversity was quantified in 224 dryland plant communities from 22 geographical regions on all continents except Antarctica using four complementary measures: the percentage of singletons (species occurring at only one site); Whittaker's beta diversity, β(W); a directional beta diversity metric based on the correlation in species occurrences among spatially contiguous sites, β(R2); and a multivariate abundance-based metric, β(MV). We used linear modelling to quantify the relationships between these metrics of beta diversity and geographical, climatic and soil variables. Results Soil fertility and variability in temperature and rainfall, and to a lesser extent latitude, were the most important environmental predictors of beta diversity. Metrics related to species identity percentage of singletons and β(W) were most sensitive to soil fertility, whereas those metrics related to environmental gradients and abundance (β(R2) and β(MV) were more associated with climate variability. Interactions among soil variables, climatic factors and plant cover were not important determinants of beta diversity. Sites receiving less than 178 mm of annual rainfall differed sharply in species composition from more mesic sites (> 200 mm). Main conclusions Soil fertility and variability in temperature and rainfall are the most important environmental predictors of variation in plant beta diversity in global drylands. Our results suggest that those sites annually receiving c. 178 mm of rainfall will be especially sensitive to future climate changes. These findings may help to define appropriate conservation strategies for mitigating effects of climate change on dryland vegetation.

Crop Yield Responses to Temperature Fluctuations in 19th Century Finland: Provincial Variation in Relation to Climate and Tree Rings

Past agricultural responses to climate variability can helps us to better understand the current and future impacts of climate change on agricultural production. We studied rye (Secale cereale) and barley (Hordeum vulgare) yield responses to temperature fluctuations in Finland during the period 1861–1913. Our analyses demonstrate the high sensitivity of non-industrialised northern agriculture to temperature anomalies. We found evidence of a strong relationship between monthly and seasonal mean temperatures and crop yields. In particular, high spring temperatures were associated with higher yields. Additionally, we tested temperature-sensitive tree-ring series for their value in indicating previous agricultural outputs. The results imply that tree-ring proxies (in particular, maximum latewood density) can provide novel material for studies of historical periods and locations where instrumentally measured climate and harvest data are not available.

Interactions of climate and land use documented in the varved sediments of Seebergsee in the Swiss Alps

This paper presents a multiproxy high-resolution study of the past 2600 years for Seebergsee, a small Swiss lake with varved sediments at the present tree-line ecotone. The laminae were identified as varves by a numerical analysis of diatom counts in the thin-sections. The hypothesis of two diatom blooms per year was corroborated by the 210Pb and 137Cs chronology. A period of intensive pasturing during the ‘Little Ice Age’ between ad 1346 and ad 1595 is suggested by coprophilous fungal spores, as well as by pollen indicators of grazing, by the diatom-inferred total phosphorus, by geochemistry and by documentary data. The subsequent re-oligotrophication of the lake took about 88 years, as determined by the timelag between the decline of coprophile fungal spores and the restoration of pre-eutrophic nutrient conditions. According to previous studies of latewood densities from the same region, cold summers around ad 1600 limited the pasturing at this altitude. This demonstrated the socio-economic impact of a single climatic event. However, the variance partitioning between the effects of land use and climate, which was applied for the whole core, revealed that climate independent of land use and time explained only 1.32% of the diatom data, while land use independent of climate and time explained 15.7%. Clearly land use in‘ uenced the lake, but land use was not always driven by climate. Other factors beside climate, such as politics or the introduction of fertilizers in the seventeenth and eighteenth centuries also in‘ uenced the development of Alpine pasturing.

The Early Spörer Minimum – A Period of Extraordinary Climate and Socio-economic Changes in Western and Central Europe

Throughout the last millennium, mankind was affected by prolonged deviations from the climate mean state. While periods like the Maunder Minimum in the 17th century have been assessed in greater detail, earlier cold periods such as the 15th century received much less attention due to the sparse information available. Based on new evidence from different sources ranging from proxy archives to model simulations, it is now possible to provide an end-to-end assessment about the climate state during an exceptionally cold period in the 15th century, the role of internal, unforced climate variability and external forcing in shaping these extreme climatic conditions, and the impacts on and responses of the medieval society in Central Europe. Climate reconstructions from a multitude of natural and human archives indicate that, during winter, the period of the early Spörer Minimum (1431–1440 CE) was the coldest decade in Central Europe in the 15th century. The particularly cold winters and normal but wet summers resulted in a strong seasonal cycle that challenged food production and led to increasing food prices, a subsistence crisis, and a famine in parts of Europe. As a consequence, authorities implemented adaptation measures, such as the installation of grain storage capacities, in order to be prepared for future events. The 15th century is characterised by a grand solar minimum and enhanced volcanic activity, which both imply a reduction of seasonality. Climate model simulations show that periods with cold winters and strong seasonality are associated with internal climate variability rather than external forcing. Accordingly, it is hypothesised that the reconstructed extreme climatic conditions during this decade occurred by chance and in relation to the partly chaotic, internal variability within the climate system.

Climate and soil characteristics and soil arthropod abundance on Anchorage, Signy and Falkland Islands

Over a 2-year study, we investigated the effect of environmental change on the diversity and abundance of soil arthropod communities (Acari and Collembola) in the Maritime Antarctic and the Falkland Islands. Open Top Chambers (OTCs), as used extensively in the framework of the northern boreal International Tundra Experiment (ITEX), were used to increase the temperature in contrasting communities on three islands along a latitudinal temperature gradient, ranging from the Falkland Islands (51°S, mean annual temperature 7.5 °C) to Signy Island (60°S, -2.3°C) and Anchorage Island (67°S, -3.8°C). At each island an open and a closed plant community were studied: lichen vs. moss at the Antarctic sites, and grass vs. dwarf shrub at the Falkland Islands. The OTCs raised the soil surface temperature during most months of the year. During the summer the level of warming achieved was 1.7 °C at the Falkland Islands, 0.7 °C at Signy Island, and 1.1 °C at Anchorage Island. The native arthropod community diversity decreased with increasing latitude. In contrast with this pattern, Collembola abundance in the closed vegetation (dwarf shrub or moss) communities increased by at least an order of magnitude from the Falkland Islands (9.0 +/- 2 x 10**3 ind./m**2) to Signy (3.3 +/- 8.0 x 10**4 ind./m**2) and Anchorage Island (3.1 +/- 0.82 x 10**5 ind./m**2). The abundance of Acari did not show a latitudinal trend. Abundance and diversity of Acari and Collembola were unaffected by the warming treatment on the Falkland Islands and Anchorage Island. However, after two seasons of experimental warming, the total abundance of Collembola decreased (p < 0.05) in the lichen community on Signy Island as a result of the population decline of the isotomid Cryptopygus antarcticus. In the same lichen community there was also a decline (p < 0.05) of the mesostigmatid predatory mite Gamasellus racovitzai, and a significant increase in the total number of Prostigmata. Overall, our data suggest that the consequences of an experimental temperature increase of 1-2°C, comparable to the magnitude currently seen through recent climate change in the Antarctic Peninsula region, on soil arthropod communities in this region may not be similar for each location but is most likely to be small and initially slow to develop.

Climate and total tree cover reconstructions based on the 43.7-kyr fossil pollen record from Khoe (NW Sakhalin Island) and modern climate variables of 236 modern surface pollen sampling sites

A late Quaternary pollen record from northern Sakhalin Island (51.34°N, 142.14°E, 15 m a.s.l.) spanning the last 43.7 ka was used to reconstruct regional climate dynamics and vegetation distribution by using the modern analogue technique (MAT). The long-term trends of the reconstructed mean annual temperature (TANN) and precipitation (PANN), and total tree cover are generally in line with key palaeoclimate records from the North Atlantic region and the Asian monsoon domain. TANN largely follows the fluctuations in solar summer insolation at 55°N. During Marine Isotope Stage (MIS) 3, TANN and PANN were on average 0.2 °C and 700 mm, respectively, thus very similar to late Holocene/modern conditions. Full glacial climate deterioration (TANN = -3.3 °C, PANN = 550 mm) was relatively weak as suggested by the MAT-inferred average climate parameters and tree cover densities. However, error ranges of the climate reconstructions during this interval are relatively large and the last glacial environments in northern Sakhalin could be much colder and drier than suggested by the weighted average values. An anti-phase relationship between mean temperature of the coldest (MTCO) and warmest (MTWA) month is documented during the last glacial period, i.e. MIS 2 and 3, suggesting more continental climate due to sea levels that were lower than present. Warmest and wettest climate conditions have prevailed since the end of the last glaciation with an optimum (TANN = 1.5 °C, PANN = 800 mm) in the middle Holocene interval (ca 8.7-5.2 cal. ka BP). This lags behind the solar insolation peak during the early Holocene. We propose that this is due to continuous Holocene sea level transgression and regional influence of the Tsushima Warm Current, which reached maximum intensity during the middle Holocene. Several short-term climate oscillations are suggested by our reconstruction results and correspond to Northern Hemisphere Heinrich and Dansgaard-Oeschger events, the Bølling-Allerød and the Younger Dryas. The most prominent fluctuation is registered during Heinrich 4 event, which is marked by noticeably colder and drier conditions and the spread of herbaceous taxa.