• Energy Research

In a recent study (1), we conducted a global synthesis of long-term records of reconstructed sediment accumulation rates (SARs) in lakes and diagnosed that a dominant anthropogenic imprint on soil erosion rates started ∼4,000 y ago. Our approach was based on the assumption that lake SARs are watershed integrators of terrestrial biogeochemical responses to atmospheric (climate) and land surface dynamics spanning several millennia (2⇓–4). Our statistical analysis was based on SAR reconstructions for the last 12,000 y (1), global pollen records spanning the same period to infer past vegetation changes (5), and model-based climate reconstructions from transient Holocene simulation with … [↵][1]1To whom correspondence may be addressed. Email: Jean-Philippe.Jenny{at}inrae.fr. [1]: #xref-corresp-1-1

In a recent study (1), we conducted a global synthesis of long-term records of reconstructed sediment accumulation rates (SARs) in lakes and diagnosed that a dominant anthropogenic imprint on soil erosion rates started ∼4,000 y ago. Our approach was based on the assumption that lake SARs are watershed integrators of terrestrial biogeochemical responses to atmospheric (climate) and land surface dynamics spanning several millennia (2⇓–4). Our statistical analysis was based on SAR reconstructions for the last 12,000 y (1), global pollen records spanning the same period to infer past vegetation changes (5), and model-based climate reconstructions from transient Holocene simulation with … [↵][1]1To whom correspondence may be addressed. Email: Jean-Philippe.Jenny{at}inrae.fr. [1]: #xref-corresp-1-1

Although widely distributed throughout Arctic and subarctic regions, thermokarst ponds and lakes remain relatively unexplored regarding geomorphological changes in their catchments and their internal properties in relation to climate change over the past decades. This study synthesizes recent landscape evolution and modern sedimentology of limnologically diverse thermokarst ponds near southeastern Hudson Bay, Canada. Spatio-temporal analysis of permafrost mounds, thermokarst ponds, and vegetation surface areas over the past five decades revealed that the recent climate-induced decrease of permafrost-affected areas was not primarily compensated by thermokarst pond development, but rather by a remarkable increase in vegetation cover. These changes appeared to be modulated by topographical and hydrological gradients at the study site, which are associated with east-ward increasing thickness of postglacial marine deposits. At a more contemporary timescale, physico-chemical measurements made on sedimenting materials (sediment traps) and freshly deposited lacustrine sediments of selected thermokarst ponds revealed striking differences both among ponds and between the oxic epilimnion and the oxygen-depleted hypolimnion. These findings underscore the major influence of local landscape properties and oxycline development on pond sedimentology and geochemistry, such as the transport of detritic particles and the concentration of redox-sensitive elements.

Although widely distributed throughout Arctic and subarctic regions, thermokarst ponds and lakes remain relatively unexplored regarding geomorphological changes in their catchments and their internal properties in relation to climate change over the past decades. This study synthesizes recent landscape evolution and modern sedimentology of limnologically diverse thermokarst ponds near southeastern Hudson Bay, Canada. Spatio-temporal analysis of permafrost mounds, thermokarst ponds, and vegetation surface areas over the past five decades revealed that the recent climate-induced decrease of permafrost-affected areas was not primarily compensated by thermokarst pond development, but rather by a remarkable increase in vegetation cover. These changes appeared to be modulated by topographical and hydrological gradients at the study site, which are associated with east-ward increasing thickness of postglacial marine deposits. At a more contemporary timescale, physico-chemical measurements made on sedimenting materials (sediment traps) and freshly deposited lacustrine sediments of selected thermokarst ponds revealed striking differences both among ponds and between the oxic epilimnion and the oxygen-depleted hypolimnion. These findings underscore the major influence of local landscape properties and oxycline development on pond sedimentology and geochemistry, such as the transport of detritic particles and the concentration of redox-sensitive elements.

AbstractReproducible climate reconstructions of the Common Era (1 CE to present) are key to placing industrial-era warming into the context of natural climatic variability. Here we present a community-sourced database of temperature-sensitive proxy records from the PAGES2k initiative. The database gathers 692 records from 648 locations, including all continental regions and major ocean basins. The records are from trees, ice, sediment, corals, speleothems, documentary evidence, and other archives. They range in length from 50 to 2000 years, with a median of 547 years, while temporal resolution ranges from biweekly to centennial. Nearly half of the proxy time series are significantly correlated with HadCRUT4.2 surface temperature over the period 1850–2014. Global temperature composites show a remarkable degree of coherence between high- and low-resolution archives, with broadly similar patterns across archive types, terrestrial versus marine locations, and screening criteria. The database is suited to investigations of global and regional temperature variability over the Common Era, and is shared in the Linked Paleo Data (LiPD) format, including serializations in Matlab, R and Python.