Early to mid‐Holocene climate change at Lago dell'Accesa (central Italy): climate signal or anthropogenic bias?

Despite the high potential of pollen records for climate reconstruction, pollen–climate relationships may be biased due to past and present human activities on the landscape. We use (i) transfer functions based on modern pollen–climate relationships to infer seasonal temperature and summer precipitation for the period 11 500–4500 cal. a BP and (ii) lake‐level change records based on different sedimentary proxies in multiple cores that are mainly indicative for summer hydrology at Lago dell'Accesa (central Italy). Quantitative reconstructions indicate lowest summer precipitation during two phases (8500–7700 cal. a BP and after 6000 cal. a BP) and a gradual winter temperature increase from 11 500 to ca. 8000 cal. a BP. Lowest summer precipitation was reconstructed during these phases characterised by vegetation shifts from open forests dominated by summergreen oaks (Quercus) to forests dominated by evergreen oaks (Quercus ilex), which are at present most abundant where summer drought is stronger. Similarly, the lake‐level record indicates two long‐lasting low summer precipitation phases (8800–7700 and 6400–4400 cal. a BP) that were interrupted by short‐term high summer precipitation events. Based on the broad agreement between the pollen‐inferred summer precipitation and the low‐frequency lake‐level changes, we suggest that the duration of the high summer precipitation events may have been too short to maintain drought‐sensitive trees, which may have been affected by high mortality rates when summer dry conditions returned. Although past and modern pollen–climate relationships may very likely have been affected by human activities since the Neolithic (i.e. when exploitation of the landscape started), we reject the hypothesis of a significant anthropogenic bias in the pollen‐based climate reconstruction. In addition, we suggest that pollen‐based and lake‐level reconstructions may have different inherent abilities of capturing high‐ and low‐frequency precipitation signals. Copyright © 2010 John Wiley & Sons, Ltd.     

A 17,900-year multi-proxy lacustrine record of Lago Puyehue (Chilean Lake District): introduction

This paper introduces the background and main results of a research project aimed at unravelling the paleolimnological and paleoclimatological history of Lago Puyehue (40° S, Lake District, Chile) since the Last Glacial Maximum (LGM), based on the study of several sediment cores from the lake and on extensive fieldwork in the lake catchment. The longest record was obtained in an 11-m-long piston core. An age-depth model was established by AMS ¹⁴C dating, ²¹⁰Pb and ²³⁷Cs measurements, identification of event-deposits, and varve-counting for the past 600 years. The core extends back to 17,915 cal. yr. BP, and the seismic data indicate that an open-lake sedimentary environment already existed several thousands of years before that. The core was submitted to a multi-proxy analysis, including sedimentology, mineralogy, grain-size, major geochemistry and organic geochemistry (C/N ratio, δ¹³C), loss-on-ignition, magnetic susceptibility, diatom analysis and palynology. Along-core variations in sediment composition reveal that the area of Lago Puyehue was characterized since the LGM by a series of rapid climate fluctuations superimposed on a long-term warming trend. Identified climate fluctuations confirm a.o. the existence of a Late-Glacial cold reversal predating the northern-hemisphere Younger Dryas cold period by 500–1,000 years, as well as the existence of an early southern-hemisphere Holocene climatic optimum. Varve-thickness analyses over the past 600 years reveal periodicities similar to those associated with the El Niño Southern Oscillation and the Pacific Decadal Oscillation, as well as intervals with increased precipitation, related to an intensification of the El Niño impact during the southern-hemisphere equivalent of the Little Ice Age.     

Airborne radar measurements of ocean wave spectra and wind speed during the grand banks ERS‐1 SAR wave experiment

Abstract

Measurements of ocean directional wave spectra, significant wave height, and wind speed over the Grand Banks of Newfoundland were made using the combined capabilities of the radar ocean wave spectrometer (ROWS) and scanning radar altimeter (SRA). The instruments were flown aboard the NASA P‐3A aircraft in support of the Grand Banks ERS‐1 Synthetic Aperture Radar (SAR) Wave Experiment. The NASA sensors use proven techniques, which differ greatly from SAR, for estimating the directional long‐wave spectrum; thus they provide a unique set of measurements for use in evaluating SAR performance. ROWS and SRA data are combined with spectra from the SAR aboard the Canadian Centre for Remote Sensing (CCRS) CV‐580 aircraft, the first‐generation Canadian Spectral Ocean Wave Model (CSOWM) hindcast, and other available in situ measurements to assess the ERS‐1 SAR's ability to correctly resolve wave field components along a 200‐ to 300‐km flight line for four separate satellite passes. Given the complex seas present on the Grand Banks, the complementary nature of viewing the sea spectrum from the perspectives of multiple sensors and a wave prediction model is apparent. The data intercomparisons show the ERS‐1 SAR to be meeting the expected goals for measuring swell, but the data also show evidence of this remote sensor's inability to detect the shorter waves travelling in the azimuth or along‐track direction. Example SAR spectra simulations are made using a non‐linear forward transform with ROWS measurements as input. Additionally, surface wind and wave height estimates made using the ROWS altimeter channel are presented. These data demonstrate the utility of operating the system in its new combined altimeter and spectrometer configuration.     

Quantity Does Not Always Mean Quality: The Importance of Qualitative Social Science in Conservation Research

Qualitative methods are important to gain a deep understanding of complex problems and poorly researched areas. They can be particularly useful to help explain underlying conservation problems. However, the significance in choosing and justifying appropriate methodological frameworks in conservation studies should be given more attention to ensure data are collected and analysed appropriately. We explain when, why, and how qualitative methods should be used and explain sampling strategies in qualitative studies. To improve familiarity with qualitative methods among natural scientists, we recommend expanding training in social sciences and increasing collaboration with social scientists. Given the scale of human impacts on the environment, this type of nuanced analytical skill is critical for progressing biodiversity conservation efforts.     

Evidence from wavelet analysis for a mid-Holocene transition in global climate forcing

A strong mid-Holocene transition has been identified by wavelet analyses in several sea ice cover records from the circum-Antarctic area, ice core records (Taylor dome, Byrd) and tropical marine records. The results are compared with those previously published in a synthesis of North Atlantic records and with 4 new records from the Norwegian and Icelandic seas and from a coastal site in Ireland. These new records confirm the previous pattern for the North Atlantic area, extend this pattern nearly to the Arctic Circle, and include a continental record. We further tested the possibility of extending this scheme using continental records from South America. The Holocene pattern proposed here confirms the importance of external forcing during the Early Holocene (solar activity: 1000 years cyclicity and 2500 years during the entire Holocene), even if the signal is disturbed by meltwater fluxes. The second part of the Holocene is then marked by the gradual appearance of internal forcing (thermohaline circulation around 1500 years), associated with a stabilisation of the signal. Coupling between ocean and atmosphere seems to play a fundamental role in the observed frequencies which vary accordingly in the Atlantic, circum-Antarctic and Pacific areas. The North Atlantic area seems to be the instigator of thermohaline circulation as shown by its sensitivity to meltwater discharges during the Early Holocene, even though each sector is independent with regards to its frequency content (around 1600 years for Atlantic Area; around 1250 years for Antarctica). The Holocene methane pattern, still under debate [Ruddiman, W.F., 2003a. Orbital insolation, ice volume and greenhouse gases. Quaternary Science Review 22, 1597–1629; Ruddiman, W.F., 2003b. The anthropogenic greenhouse era began thousands of years ago. Climatic Change 61, 261–293], could be explained by a more efficient thermohaline circulation around the mid-Holocene with an anthropogenic effect initiated at 2500 BP as shown by the inter-hemispheric gradient.     

Geophysical flows under location uncertainty,Part III SQG and frontal dynamics under strong turbulence conditions

Models under location uncertainty are derived assuming that a component of the velocity is uncorrelated in time. The material derivative is accordingly modified to include an advection correction, inhomogeneous and anisotropic diffusion terms and a multiplicative noise contribution. This change can be consistently applied to all fluid dynamics evolution laws. This paper continues to explore benefits of this framework and consequences of specific scaling assumptions. Starting from a Boussinesq model under location uncertainty, a model is developed to describe a mesoscale flow subject to a strong underlying submesoscale activity. Specifically, turbulent diffusion and rotation effects have similar orders of magnitude. As obtained, the geostrophic balance is modified and the Quasi-Geostrophic assumptions remarkably lead to a zero Potential Vorticity. The ensuing Surface Quasi-Geostrophic model provides a simple diagnosis of warm frontolysis and cold frontogenesis.     

Monitoring short-period internal waves in the White Sea

Widespread short-period internal wave (SPIW) activity in the White Sea has been revealed for the first time based on long-term (2009–2013) monitoring performed using satellite and in situ observations, and the statistical characteristics of these waves have been obtained. Two main regions where short-period waves constantly exist have been identified: the shelf area near the frontal zone at the boundary between the Basin and the Gorlo Strait and the shallow shelf area where the depths are about 30–50 m near Solovetskie Islands. Intense internal waves (IIWs), which are substantially nonlinear and are related to specific phases of a barotropic tide, are regularly observed near frontal zones. The wave height can reach half the sea depth and the wave periods vary from 7 to 18 min.     

Detailed seismic stratigraphy of Lago Puyehue: implications for the mode and timing of glacier retreat in the Chilean Lake District

Lago Puyehue is a glacigenic lake in the Chilean Lake District (40°S) with a complex deglaciation history. A detailed seismic–stratigraphic study of its sedimentary infill indicates a much earlier retreat of the glacier from the Lago Puyehue basin than the neighbouring glacier from the Lago Rupanco basin. Because of their close proximity, Rupanco meltwater streams played an important part in the depositional processes of Lago Puyehue. A timing discrepancy between the in‐lake ages of a sediment core and the outer‐lake ages of moraine deposits (re)opens the discussion on the timing of deglaciation in the Southern Hemisphere. Copyright © 2011 John Wiley & Sons, Ltd.     

Submesoscale Eddies in the White Sea Based on Satellite Radar Measurements

Izvestiya, Atmospheric and Oceanic Physics - This paper presents the results of the analysis of the archive of radar images of Envisat Advanced Synthetic Aperture Radar (ASAR) and Radarsat-1,2 for...     

Features of wind field over the sea surface in the coastal area

In this paper we analyze SAR wind field features, in particular the effects of wind shadowing. These effects represent the dynamics of the internal atmospheric boundary layer, which is formed due to the transition of the air flow arriving from the rough land surface to the “smooth” water surface. In the wind-shadowed area, the flow accelerates, and a surface wind stress increases with fetch. The width of the shadow depends not only on the wind speed and atmospheric boundary layer stratification, but also on geographic features such as windflow multiple transformations over the complex surface land–Lake Chudskoe–land–Gulf of Finland. Measurements showed that, in the area of wind acceleration, the surface stress normalized by an equilibrium value (far from the coast) is a universal function of dimensionless fetch Xf/G. Surface wind stress reaches an equilibrium value at Xf/G ≈ 0.4, which is the scale of the planetary-boundary-layer relaxation.