Gesine Mollenhauer

Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research | AWI · Department of Marine Geochemistry

Establishing accurate chronological frameworks is imperative for reliably identifying lead–lag dynamics within the climate system and enabling meaningful intercomparisons across diverse paleoclimate proxy records over long time periods. Robust age models provide a solid temporal foundation for establishing correlations between paleoclimate records....

Intense convective mixing in the central North Atlantic is a major gateway for dissolved organic matter (DOM) into the deep ocean, sustaining elevated dissolved organic carbon (DOC) concentrations. Rapid down‐slope transport on adjacent Irish and Hebrides Margins represents another, less‐explored mechanism contributing to the deep‐sea DOM reservoir...

The Eifel Volcanic Field (EVC) is one of the best-known intraplate volcanic fields on earth. Carbonatitic ejecta were already described at the beginning of the last century and were associated with volcanism. The investigation of carbonatitic tephra from the EVC, the Kaiserstuhl (KVC) and El Hierro (EHSR) with regard to shape, size, composition and...

Arctic permafrost stores vast amounts of terrestrial organic matter (terrOM). Under warming climate conditions, Arctic permafrost thaws, releasing aged carbon and potentially impacting the modern carbon cycle. We investigated the characteristics of terrestrial biomarkers, including n-alkanes, fatty acids, and lignin phenols, in marine sediment core...

The Siberian Arctic is warming rapidly, causing permafrost to thaw and altering the biogeochemistry of aquatic environments, with cascading effects on the coastal and shelf ecosystems of the Arctic Ocean. The Lena River, one of the largest Arctic rivers, drains a catchment dominated by permafrost. Baseline discharge biogeochemistry data is necessar...

The Arctic is experiencing rapid warming, which among other processes results in increasing erosion of coastal permafrost and the release of ancient organic carbon (OC) into the Arctic Ocean, which in turn might result in greenhouse gas emissions following its decomposition. Supply of terrigenous organic matter to the ocean affects near‐shore nutri...

Ratios of glycerol dialkyl glycerol tetraethers (GDGT), which are membrane lipids of bacteria and archaea, are at the base of several paleoenvironmental proxies. They are frequently applied to soils as well as lake‐ and marine sediments to generate records of past temperature and soil pH. To derive meaningful environmental information from these re...

Carbon storage in soils is important in regulating atmospheric carbon dioxide (CO2). However, the sensitivity of the soil-carbon turnover time (τsoil) to temperature and hydrology forcing is still not fully understood. Here, we use radiocarbon dating of plant-derived lipids in conjunction with reconstructions of temperature and rainfall from an eas...

Establishing accurate chronological frameworks is imperative for reliably identifying lead-lag dynamics within the climate system and enabling meaningful inter-comparisons across diverse paleoclimate proxy records over long time periods. Robust age models provide a solid temporal foundation for establishing correlations between paleoclimate records...

On behalf of the authors and readers of Reviews of Geophysics (RoG), the American Geophysical Union, and the broader scientific community, the editors wish to wholeheartedly thank those who reviewed manuscripts for RoG in 2023.

Between 14.5 and 5 ka, the Sahara was vegetated owing to a wet climate during the African humid period. However, the climatic factors sustaining the “green Sahara” are still a matter of debate. Particularly the role of winter precipitation is poorly understood. Using the stable hydrogen isotopic composition (δD, where D stands for deuterium) of hig...

In Antarctica, the presence of sea ice in front of ice shelves promotes their stability and prevents the risk of catastrophic collapse as witnessed in recent events along the Antarctic Peninsula. Investigating past ice-proximal sea-ice conditions, especially across glacial-interglacial cycles, can provide crucial information pertaining to sea-ice v...

The last deglaciation is the most recent relatively well-documented period of pronounced and fast climate warming, and, as such, it holds important information for our understanding of the climate system. Notably, while research into terrestrial organic carbon reservoirs has been instrumental in exploring the possible sources of atmospheric carbon...

Human activities have increasingly changed terrestrial particulate organic carbon (POC) export to the coastal ocean since the Industrial Age (19th century). However, the influence of human perturbations on the composition and flux of terrestrial biospheric and petrogenic POC sub‐pools remains poorly constrained. Here, we examined ¹³C and ¹⁴C compos...

The Bølling-Allerød interstadial (14,700–12,900 years before present), during the last deglaciation, was characterized by rapid warming and sea level rise. Yet, the response of the Arctic terrestrial cryosphere during this abrupt climate change remains thus far elusive. Here we present a multi-proxy analysis of a sediment record from the northern S...

Rock-derived or petrogenic organic carbon has traditionally been regarded as being non-bioavailable and bypassing the active carbon cycle when eroded. However, it has become apparent that this organic carbon might not be so inert, especially in fjord systems where petrogenic organic carbon influxes can be high, making its degradation another potent...

The reconstruction of past sea-ice distribution in the Southern Ocean is crucial for an improved understanding of ice–ocean–atmosphere feedbacks and the evaluation of Earth system and Antarctic ice sheet models. The Antarctic Peninsula (AP) has been experiencing a warming since the start of regular monitoring of the atmospheric temperature in the 1...

Plain Language Summary On behalf of the authors and readers of Reviews of Geophysics (RoG), the American Geophysical Union, and the broader scientific community, the editors wish to wholeheartedly thank those who reviewed manuscripts for RoG in 2022.

The Bølling-Allerød interstadial (14.7-12.9 kyr BP), during the last deglaciation, was characterized by rapid retreat of ice sheets and significant sea level rise (Meltwater Pulse 1A, MWP-1A; 14.7-14.3 kyr BP). Yet, the response of the terrestrial cryosphere during this period of abrupt climate change remains elusive. Here we present a multi-proxy...

Between 11.5 and 5 ka BP, the Sahara was vegetated owing to a wet climate during the African Humid Period (AHP). However, the climatic factors sustaining the “Green Sahara” are still a matter of debate. Particularly the role of winter precipitation is poorly understood. Using the stable hydrogen isotopic composition (δD) of high molecular weight (H...

As calcareous foraminifera precipitate their shells from the surrounding water mass, they are the basis of most marine radiocarbon chronologies and paleo-proxies. Nevertheless, post-mortem alteration of shells, especially addition of authigenic calcite, impact proxy records. In the Arctic Ocean, authigenic calcite overgrowth on foraminifera has bee...

Rapid Arctic warming accelerates permafrost thaw, causing an additional release of terrestrial organic matter (OM) into rivers and, ultimately, after transport via deltas and estuaries, to the Arctic Ocean nearshore. The majority of our understanding of nearshore OM dynamics and fate has been developed from freshwater rivers despite the likely impa...

Reviews of Geophysics is an AGU journal, first established in February 1963. It is a hybrid open access invitation‐only journal that publishes comprehensive review articles across various disciplines within the Earth and Space Sciences. The selection criteria are rigorous and many submissions are declined without review. The journal is the highest...

The last deglaciation is the most recent relatively well-documented period of pronounced and fast climate warming and, as such, it holds important information for our understanding of the climate system. Notably, while research into terrestrial organic carbon reservoirs has been instrumental in exploring the possible sources of atmospheric carbon d...

Glacial legacies preserved in permafrost such as buried glacial ice of the last ice age are of increasing concern in the Western Canadian Arctic. Permafrost collapse due to melting ground ice largely follows the margins of the maximum Laurentide Ice Sheet extent and therefore predetermines the postglacial landscape evolution in this region. Another...

Arctic warming and sea level change will lead to widespread permafrost thaw and subsequent mobilization. Sedimentary records of past warming events during the Last Glacial–interglacial transition can be used to study the conditions under which permafrost mobilization occurs and which changes in vegetation on land are associated with such warming. T...

Reliable radiocarbon (14C) ages of foraminifera are a prerequisite to generate robust high-resolution age-depth models or to obtain precise understanding of past carbon cycle dynamics. With the advance of small-scale 14C measurements, instrumental precision and levels of contamination (extraneous carbon introduced during sample pretreatment or anal...

The changes in atmospheric pCO2 provide evidence for the release of large amounts of ancient carbon during the last deglaciation. However, the sources and mechanisms that contributed to this process remain unresolved. Here, we present evidence for substantial ancient terrestrial carbon remobilization in the Canadian Arctic following the Laurentide...

Rapid Arctic warming accelerates permafrost thaw, causing an additional release of terrestrial organic matter (OM) 15 into rivers, and ultimately, after transport via deltas and estuaries, to the Arctic Ocean nearshore. The majority of our understanding of nearshore OM dynamics and fate has been developed from freshwater rivers, despite the likely...

Arctic warming and sea level change will lead to widespread permafrost thaw and subsequent mobilization. Sedimentary records of past warming events during the last glacial–interglacial transition can be used to study the conditions under which permafrost mobilization occurs. Long-chain n-alkyl lipids and lignin phenols are two types of biomarkers e...

Despite the increased number of paleoceanographic studies in the SW Atlantic in recent years, the mechanisms controlling marine productivity and terrestrial material delivery to the South Brazil Bight remain unresolved. Because of its wide continental shelf and abrupt change in coastline orientation, this region is under the influence of several en...

Recent research has challenged the traditional view of rock-derived or petrogenic organic carbon (OC petro ) as non-bio-available and bypassing the active carbon cycle when eroded and buried in marine sediments ¹ and identified it as a potential source of fossil greenhouse gas emissions to the atmosphere ² . Due to rising global temperatures, glaci...

We present a global atlas of downcore foraminiferal oxygen and carbon isotope ratios available at 10.1594/PANGAEA.936747 (Mulitza et al., 2021a). The database contains 2106 published and previously unpublished stable isotope downcore records with 361 949 stable isotope values of various planktic and benthic species of Foraminifera from 1265 sedimen...

Reviews of Geophysics is the top‐rated journal in Geochemistry and Geophysics (ISI Web of Knowledge category) reflecting the many excellent contributions we received. It is an important milestone achieved with the reviewers' investment of time and effort. Their expertise ensures that the papers published in this journal meet the standards that the...

Organic carbon (OC) stored in Arctic permafrost represents one of Earth's largest and most vulnerable terrestrial carbon pools. Amplified climate warming across the Arctic results in widespread permafrost thaw. Permafrost deposits exposed at river cliffs and coasts are particularly susceptible to thawing processes. Accelerating erosion of terrestri...

Proxies based on long-chain alkane-1, mid-chain diols (diol for short) are obtaining increasing interest to reconstruct past upper ocean temperature and productivity. Here we evaluate performance of the sea surface temperature proxies (long-chain diol index (LDI), diol saturation index (DSI), and diol chain length index (DCI)), productivity and upw...

The Central Arctic Ocean is one of the most oligotrophic oceans on Earth because of its sea-ice cover and short productive season. Nonetheless, across the peaks of extinct volcanic seamounts of the Langseth Ridge (87°N, 61°E), we observe a surprisingly dense benthic biomass. Bacteriosponges are the most abundant fauna within this community, with a...

We discuss present and developing techniques for studying radiocarbon in marine organic carbon (C). Bulk DOC (dissolved organic C) Δ ¹⁴ C measurements reveal information about the cycling time and sources of DOC in the ocean, yet they are time consuming and need to be streamlined. To further elucidate the cycling of DOC, various fractions have been...

The Arctic is rich in aquatic systems and experiences rapid warming due to climate change. The accelerated warming causes permafrost thaw and the mobilization of organic carbon. When dissolved organic carbon is mobilized, this DOC can be transported to aquatic systems and degraded in the water bodies and further downstream. Here, we analyze the inf...

The Arctic is nutrient limited, particularly by nitrogen, and is impacted by anthropogenic global warming which occurs approximately twice as fast compared to the global average. Arctic warming intensifies thawing of permafrost-affected soils releasing their large organic nitrogen reservoir. This organic nitrogen reaches hydrological systems, is re...

Organic carbon (OC) stored in Arctic permafrost represents one of Earth’s largest and most vulnerable terrestrial carbon pools. Amplified climate warming across the Arctic results in widespread permafrost thaw. Permafrost deposits exposed at river cliffs and coasts are particularly susceptible to thawing processes. Accelerating erosion of terrestri...

Arctic warming is causing ancient perennially frozen ground (permafrost) to thaw, resulting in ground collapse, and reshaping of landscapes. This threatens Arctic peoples' infrastructure, cultural sites, and land-based natural resources. Terrestrial permafrost thaw and ongoing intensification of hydrological cycles also enhance the amount and alter...

The recent expansion of Atlantic waters into the Arctic Ocean represents undisputable evidence of the rapid changes occurring in this region. Understanding the past variability of this “Atlantification” is thus crucial in providing a longer perspective on the modern Arctic changes. Here, we reconstruct the history of Atlantification along the ea...

We present a global atlas of downcore foraminiferal oxygen and carbon isotope ratios available at https://doi.pangaea.de/10.1594/PANGAEA.936747 (Mulitza et al., 2021). The database contains 2,108 published and previously unpublished stable isotope downcore records with 362,067 stable isotope values of various planktonic and benthic species of foram...

Long-chain mid-chain diol (shortly diol) based proxies obtain increasing interest to reconstruct past upper ocean temperature and productivity. Here we evaluate performance of the sea surface temperature proxies; long chain diol index (LDI), the diol saturation index (DSI) and the diol chain-length index (DCI), productivity/upwelling intensity prox...

The importance of Antarctic sea ice and Southern Ocean warming has come into the focus of polar research during the last couple of decades. Especially around West Antarctica, where warm water masses approach the continent and where sea ice has declined, the distribution and evolution of sea ice play a critical role in the stability of nearby ice sh...

Marine sedimentary records are a key archive when reconstructing past climate; however, mixing at the seabed (bioturbation) can strongly influence climate records, especially when sedimentation rates are low. By commingling the climate signal from different time periods, bioturbation both smooths climate records, by damping fast climate variations,...

The radiocarbon analysis laboratory at Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research (AWI) is equipped with an accelerator mass spectrometer (AMS) MICADAS (MIni CArbon Dating System). The laboratory provides routine ¹⁴C analyses on bulk organic matter, plant fragments, dissolved and particulate organic matter, individual m...

Sedimentary high molecular weight (HMW) n-alkyl lipids derived from the waxes of terrestrial plants are common target compounds in biogeochemical and paleoenvironmental research. These plant waxes derive predominantly from the epicuticular cover of vascular plant leaves and their relative and absolute abundances and stable isotopic composition can...

Plain Language Summary The geochemical signature of stable isotopes of permafrost ground ice preserves information about past climate conditions. A common type of ground ice is ice wedges that form by the freezing of snowmelt in frost cracks developed on the ground and grow over time in width and length. Winter temperatures, and the type (snow or r...

Tropical and subtropical rivers deliver large quantities of terrestrial organic carbon (OCterr) to the ocean, acting as a crucial part of the global carbon cycle, but little is known about the timescale and efficiency of its transport to and in the adjacent coastal sea. Here we examined source-specific biomarker (fatty acids, FAs) contents and isot...

Plain Language Summary On behalf of the authors and readers of Reviews of Geophysics (RoG), the American Geophysical Union (AGU), and the broader scientific community, the editors wish to wholeheartedly thank those who reviewed manuscripts for RoG in 2020.

In a warming climate, thawing permafrost soils in the circumpolar Arctic region are subject to enhanced microbial turnover as well as mass mobilization and other erosion processes. High‐Arctic settings such as Svalbard are exceptionally vulnerable to these effects, but the presence of coal deposits obscures the organic carbon (OC) signature of perm...

The importance of Southern Ocean sea ice has come into the focus of polar research in the last couple of decades. Especially in West Antarctica, where sea ice has declined, its distribution and evolution play a critical role for the stability of nearby ice shelves. Organic geochemical analyses of marine surface sediments from the West Antarctic con...