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We review the approaches for estimating biomass burning from ice-cores and consider the challenges and assumptions in their application. In particular, we consider the potential of biomarker proxies for biomass burning, hitherto not widely applied to glacial ice archives. We also review the available records of biomass burning in ice-cores and consider how variations in fire regimes have been related to atmospheric and land-use changes. Finally, we suggest that future developments in ice-core science should aim to combine multiple biomarkers with other records (black carbon, charcoal) and models to discern the types of material being burnt (C3versus C4plants, angiosperms, gymnosperms, peat fires, etc.) and to improve constraints on source areas of biomass burning. An ultimate goal is to compare the biomass burning record from ice-cores with hindcasts from models to project how future climate change will influence biomass burning and, inversely, how fire will affect climate.

AbstractPlant waxes (e.g. long-chain n-alkanes) in ice cores are a promising paleovegetation proxy. However, much work needs to be done to assess how n-alkanes are transported from source areas to, and incorporated into, glacial archives. In this paper we present analyses of n-alkanes in seasonal snow and assess the information on source vegetation. n-Alkanes with carbon numbers C18to C43were extracted from snow samples collected at two sites in Hokkaido, northern Japan, during winter 2009–2010. Molecular distributions revealed that the majority of the n-alkanes originated from higher vegetation (ca. 65%), rather than anthropogenic sources. The distribution characteristics confirmed that the n-alkane signal had a wide regional origin, rather than a local source. We determined stable carbon and hydrogen isotopic compositions for the C27n-alkane. The δ13C of the C27( -28.2 to -33.0‰) was more representative of C3than C4vegetation, while the δD of the C27(- 169.9 to -223.1‰) indicated growth latitudes more northerly than Hokkaido. The n-alkanes in the snow preserve information about the source vegetation type (photosynthetic group, growth site), confirming that if deposited with seasonal snows that firnify to form glacial ice, they have potential to record broad, regional vegetation changes over time.

Terrestrial organic carbon (TerrOC) acts as an important CO2sink when transported via rivers to the ocean and sequestered in coastal marine sediments. This mechanism might help to modulate atmospheric CO2levels over short‐ and long‐ timescales (103–106years), but its importance during past warm climates remains unknown. Here we use terrestrial biomarkers preserved in coastal marine sediment samples from Wilkes Land, East Antarctica (∼67°S) to quantify TerrOC burial during the early Eocene (∼54.4–51.5 Ma). Terrestrial biomarker distributions indicate the delivery of plant‐, soil‐, and peat‐derived organic carbon (OC) into the marine realm. Mass accumulation rates of plant‐ (long‐chain n‐alkane) and soil‐derived (hopane) biomarkers dramatically increase between the earliest Eocene (∼54 Ma) and the early Eocene Climatic Optimum (EECO; ∼53 Ma). This coincides with increased OC mass accumulation rates and indicates enhanced TerrOC burial during the EECO. Leaf wax δ2H values indicate that the EECO was characterized by wetter conditions relative to the earliest Eocene, suggesting that hydroclimate exerts a first‐order control on TerrOC export. Our results indicate that TerrOC burial in coastal marine sediments could have acted as an important negative feedback mechanism during the early Eocene, but also during other warm climate intervals. Organic matter from the terrestrial biosphere can be transferred into rivers and eventually deposited in the ocean. This process helps to remove carbon dioxide from the atmosphere over long (>1,000 years) timescales. However, the importance of this process in warm climates is one of the most poorly understood aspects of the climate system. One way to test the behavior of the Earth in warmer‐than‐present climate states is to examine the geological record. Here we analyzed marine sediments deposited close to the Antarctic shoreline to quantify organic carbon burial during an ancient warm interval (the early Eocene, 56 to 48 million years ago). We analyzed biomolecules from plants and microbes to determine how much organic matter was derived from the terrestrial biosphere. We found evidence for increased terrestrial organic carbon burial in marine sediments during the early Eocene. This process could help to remove carbon dioxide from the atmosphere and is relevant to other episodes of climate change during Earth’s history. Terrestrial organic carbon is an important CO2sink when transported via rivers to the ocean and sequestered in coastal marine sedimentsBiomarkers indicate enhanced terrestrial organic carbon burial during early Eocene—this could have acted as a negative feedback mechanismHydrology regulates organic carbon export from the terrestrial biosphere at this site Terrestrial organic carbon is an important CO2sink when transported via rivers to the ocean and sequestered in coastal marine sediments Biomarkers indicate enhanced terrestrial organic carbon burial during early Eocene—this could have acted as a negative feedback mechanism Hydrology regulates organic carbon export from the terrestrial biosphere at this site

Recent time‐series from sediment traps show abnormally high chlorophyll‐aconcentrations and primary productivity in the oligotrophic central South China Sea (SCS), especially during wintertime. Here we present new insights from compound‐specific hydrogen isotopic analysis of leaf wax n‐alkanes and Sr‐Nd isotope compositions extracted from four basin‐wide surface sediment transects. We find that the deepest surface sediments in the central basin contain the most depleted n‐alkane hydrogen isotopes, suggesting inputs from higher latitude soils in northern China. This is supported by the Sr‐Nd isotope compositions of the same surface sediments. We propose that aeolian dust is transported by the winter monsoon and might fertilize the phytoplankton bloom in the central SCS. This process may have been enhanced in ancient times when the winter monsoon was stronger, driving both vertical mixing and dust transport to the central basin. Recent studies observe abnormally high winter primary productivity and nitrate concentrations in the surface waters of the central South China Sea (SCS). However, this is a nutrient limited region of the ocean, so the drivers of this primary productivity are unclear. Here we analyze leaf wax carbon and hydrogen isotopes, and Sr‐Nd isotopes, along four shallow‐to‐deep‐water sediment transects to trace the sources of dust and organic matter in the sediments of the central basin. Our results suggest the central basin sediments receive significant terrestrial inputs of dust and nutrients from northern Asia via long‐range aeolian transport during the winter monsoon. These results give new insights to terrestrial‐marine connections and the carbon cycle of the SCS. This process may provide a new mechanism to understand the glacial‐interglacial productivity changes in marginal seas. High concentrations of leaf‐wax n‐alkanes are observed in the South China Sea (SCS) central basinn‐Alkane carbon preference index and hydrogen isotopic composition trace aeolian dust deposition from higher latitudes to the central basinAeolian dust plays a significant role in regulating deposition of terrestrial organic matter in the central SCS High concentrations of leaf‐wax n‐alkanes are observed in the South China Sea (SCS) central basin n‐Alkane carbon preference index and hydrogen isotopic composition trace aeolian dust deposition from higher latitudes to the central basin Aeolian dust plays a significant role in regulating deposition of terrestrial organic matter in the central SCS