Past Climatic Events Research Articles

Recent flood management efforts obscure the climate signal in a sediment record from a tropical lake

Lake sediment cores contain useful archives of severe past climate events (e.g. droughts, hurricanes, dust storms) and patterns of global climate change. Most such records come from higher latitudes in the Northern Hemisphere. Here we present sediment core data from shallow, equatorial Lake La Tembladera on the southern coast of Ecuador, which contains a > 100-year record of flooding events. We used geochemical properties of a 210Pb-dated sediment core to identify two distinct sedimentary facies. Facies one represents lake-derived deposits and is characterized by sediments with relatively higher organic matter and nitrogen content. Facies two represents flood events and is characterized by sediments with greater concentrations of inorganic carbon and terrigenous elements Al and Ti. Pollen from introduced Pinus sp. and Hg associated with recent gold mining provided independent time-markers in the sediment to validate the 210Pb chronology. The comparisons of the geochemical signal with the ENSO reconstructions revealed that the sediments contain a poor signal of ENSO from AD 1930–1965. The weak ENSO signal may result from minimal climate sensitivity in the lake or early water control efforts (e.g. rudimentary damming). However, from AD 1965, the climate signal is totally masked by recent and documented anthropogenic works such as dams and canals. This record shows how anthropogenic efforts to minimize societal impacts of ENSO floods have masked the natural climate signal and nicely mirrored recent trends between climate and anthropogenic activities in tropical latitudes.

Comments on “The coastal ridge sequence at Rio Grande do Sul: A new geoarchive for past climate events of the Atlantic coast of southern Brazil since the mid Holocene” by Milana J.P., Guedes C.C.F. and Buso V.V. 2016 (Quaternary international 438, 187–199, https://doi.org/10.1016/j.quaint.2016.11.029)

The paper of Milana et al. (2016) presented interesting palaeoclimatic results related to the evolution of a foredune ridge plain of a regressive (prograded) barrier in southern Brazil. Unfortunately, they presented an evolutionary model for a type of wave-dominated delta, and not for a coastal barrier. By not classifying the regressive barrier of Cassino properly, the authors made a succession of incorrect interpretations, such as the nature of littoral drift directions during the progradation of the ridge plain. By using their delta model, they obtained opposite directions than the actual ones. In challenging the barrier model of the area, which has been well-established for more than 50 years, they should have more fully discussed the differences between deltas and barrier systems, in a manner which would have given support to their interpretations.

Genetic signature of Last Glacial Maximum regional refugia in a circum-Antarctic sea spider.

The evolutionary history of Antarctic organisms is becoming increasingly important to understand and manage population trajectories under rapid environmental change. The Antarctic sea spider Nymphon australe, with an apparently large population size compared with other sea spider species, is an ideal target to look for molecular signatures of past climatic events. We analysed mitochondrial DNA of specimens collected from the Antarctic continent and two Antarctic islands (AI) to infer past population processes and understand current genetic structure. Demographic history analyses suggest populations survived in refugia during the Last Glacial Maximum. The high genetic diversity found in the Antarctic Peninsula and East Antarctic (EA) seems related to multiple demographic contraction–expansion events associated with deep-sea refugia, while the low genetic diversity in the Weddell Sea points to a more recent expansion from a shelf refugium. We suggest the genetic structure of N. australe from AI reflects recent colonization from the continent. At a local level, EA populations reveal generally low genetic differentiation, geographically and bathymetrically, suggesting limited restrictions to dispersal. Results highlight regional differences in demographic histories and how these relate to the variation in intensity of glaciation–deglaciation events around Antarctica, critical for the study of local evolutionary processes. These are valuable data for understanding the remarkable success of Antarctic pycnogonids, and how environmental changes have shaped the evolution and diversification of Southern Ocean benthic biodiversity.

Palaeoenvironmental and diagenetic reconstruction of a closed‐lacustrine carbonate system – the challenging marginal setting of the Miocene Ries Crater Lake (Germany)

AbstractChemostratigraphic studies on lacustrine sedimentary sequences provide essential insights on past cyclic climatic events, on their repetition and prediction through time. Diagenetic overprint of primary features often hinders the use of such studies for palaeoenvironmental reconstruction. Here the potential of integrated geochemical and petrographic methods is evaluated to record freshwater to saline oscillations within the ancient marginal lacustrine carbonates of the Miocene Ries Crater Lake (Germany). This area is critical because it represents the transition from shoreline to proximal domains of a hydrologically closed system, affected by recurrent emergent events, representing the boundaries of successive sedimentary cycles. Chemostratigraphy targets shifts related to subaerial exposure and/or climatic fluctuations. Methods combine facies changes with δ13C–δ18O chemostratigraphy from matrix carbonates across five closely spaced, temporally equivalent stratigraphic sections. Isotope composition of ostracod shells, gastropods and cements is provided for comparison. Cathodoluminescence and back‐scatter electron microscopy were performed to discriminate primary (syn‐)depositional, from secondary diagenetic features. Meteoric diagenesis is expressed by substantial early dissolution and dark blue luminescent sparry cements carrying negative δ13C and δ18O. Sedimentary cycles are not correlated by isotope chemostratigraphy. Both matrix δ13C and δ18O range from ca −7·5 to +4·0‰ and show clear positive covariance (R = 0·97) whose nature differs from that of previous basin‐oriented studies on the lake: negative values are here unconnected to original freshwater lacustrine conditions but reflect extensive meteoric diagenesis, while positive values probably represent primary saline lake water chemistry. Noisy geochemical curves relate to heterogeneities in (primary) porosity, resulting in selective carbonate diagenesis. This study exemplifies that ancient lacustrine carbonates, despite extensive meteoric weathering, are able to retain key information for both palaeoenvironmental reconstruction and the understanding of diagenetic processes in relation to those primary conditions. Also, it emphasizes the limitation of chemostratigraphy in fossil carbonates, and specifically in settings that are sensitive for the preservation of primary environmental signals, such as lake margins prone to meteoric diagenesis.

Marine sediment cores database for the Mediterranean Basin: a tool for past climatic and environmental studies

AbstractPaleoclimatic data are essential for fingerprinting the climate of the earth before the advent of modern recording instruments. They enable us to recognize past climatic events and predict future trends. Within this framework, a conceptual and logical model was drawn to physically implement a paleoclimatic database named WDB-Paleo that includes the paleoclimatic proxies data of marine sediment cores of the Mediterranean Basin. Twenty entities were defined to record four main categories of data: a) the features of oceanographic cruises and cores (metadata); b) the presence/absence of paleoclimatic proxies pulled from about 200 scientific papers; c) the quantitative analysis of planktonic and benthonic foraminifera, pollen, calcareous nannoplankton, magnetic susceptibility, stable isotopes, radionuclides values of about 14 cores recovered by Institute for Coastal Marine Environment (IAMC) of Italian National Research Council (CNR) in the framework of several past research projects; d) specific entities recording quantitative data on

Data, Models and Earth History in Deep Convolution: Paleoclimate Simulations and their Epistemological Unrest.

Data, Models and Earth History in Deep Convolution: Paleoclimate Simulations and their Epistemological Unrest. Climate and Earth system models are not only used to project future conditions but also to re-construct past climatic events. This is the second in a series of papers1 that argue that paleoclimatology, the study of climate prior to the period of direct, instrumental measurements, is an epistemically radical field, one which directly abolishes the distinction between data and model, and reconfigures the notion of experiment. In doing so our notion of deep (or geological) and shallow (or historical) time has become convoluted. The present paper shows, first, how the introduction of general circulation models not only shifted the analysis of the complex causes and processes of ancient climatic change toward numerical simulation techniques, but also how this very introduction was accompanied, if not also fundamentally impacted upon, by paleoclimatic questions in the first place. Second, these computer experiments, and the temporal processes and scales they make operative, turn out to be a potent catalyst in bringing about a new sense of the temporality in which our present transition into the Anthropocene unfolds. By discussing the historical development of paleoclimate modeling, and through examining the productive heuristic qualities of its practices, this paper introduces the unconventional and pragmatic episteme by which paleoclimate simulation challenges our fixation with the category of uncertainty.

North‐west Africa as a source and refuge area of plant biodiversity: a case study on Campanula kremeri and Campanula occidentalis

AbstractAimNorth‐west Africa, because of its position at the crossroads between Macaronesia and the Iberian Peninsula, has played an important role on the emergence and maintenance of Mediterranean plant diversity. In this study, we reconstruct the phylogeographical history of a lineage of bellflowers comprising the north African‐south Iberian species Campanula kremeri and the Canarian Campanula occidentalis (Azorina‐group), to investigate the genetic imprints left by past climatic and palaeogeographical events on the northern African flora.LocationNorth‐west Africa, Iberian Peninsula, and the Canary Islands.MethodsWe reconstructed the biogeographical history of the Azorina‐group to provide a phylogenetic background. We then investigated the phylogeographical patterns within C. kremeri and C. occidentalis using the AFLP and sequence data. We integrated these results with the past species‐distribution modelling to understand the current biodiversity patterns within this lineage.ResultsThe ancestor of C. kremeri‐C. occidentalis diverged in the Late Miocene/Early Pliocene. Nuclear data supported species monophyly, whereas plastid data suggested that C. kremeri is paraphyletic. Maghrebian populations of C. kremeri showed high genetic diversity, whilst Iberian ones and those of C. occidentalis exhibited lower values.Main conclusionsRepeated expansion‐retraction events associated with Pleistocene climatic changes in North Africa facilitated gene flow across Maghrebian ranges in C. kremeri. Mountain massifs in north‐west Africa likely acted as refugia for Mediterranean plants during interglacial periods, whereas range expansion in cooler periods triggered dispersal to neighbouring regions. The range of C. kremeri expanded to the Iberian Peninsula by long‐distance dispersal across the Strait of Gibraltar during the Pleistocene. The relatively old age inferred for C. occidentalis together with its low genetic diversity point to a recent colonization of the Canary Islands from north‐west Africa followed by extinction in the mainland or an old lineage that underwent a recent genetic bottleneck.

Freshwater diatoms in the Sajama, Quelccaya, and Coropuna glaciers of the South American Andes

Diatoms in ice cores have been used to infer regional and global climatic events. These archives offer high-resolution records of past climate events, often providing annual resolution of environmental variability during the Late Holocene. Recently, the first low-latitude tropical diatoms were described from the Quelccaya Summit Dome. Here, we document diatoms observed in ice cores from Quelccaya, spanning AD 1300 to 1815, along with those from two additional glaciers (Coropuna, and Sajama glaciers) in the tropical Andes, spanning AD 1764 to 1814. Diatom assemblages recovered from these three sites were rare, but differ in abundance and species composition through time. Assemblages are characterized by cosmopolitan and aerophilic species, mostly pennate diatoms. There were 44 taxa in all, with Pinnularia cf. borealis Ehrenberg being the most common species encountered in the samples. Eleven taxa were found at all three sites. Both Coropuna and Sajama had taxa that were unique to these locations, whereas Quelccaya had no unique taxa. Due to the rarity of diatoms and the cosmopolitan nature of the dominant species, it is not possible to determine their origin, limiting their utility in paleoclimate reconstructions.

The coastal ridge sequence at Rio Grande do Sul: A new geoarchive for past climate events of the Atlantic coast of southern Brazil since the mid Holocene

Abstract We present here the first geochronometric analysis of a large succession of coastal ridges that developed south of Rio Grande do Sul inlet, aided by OSL dating of samples taken in this succession that amounts c. 306 coastal ridges. This succession allows defining epochs of enhanced coastal drift or fluvial transport to the river mouth. Additionally, changes in the preservation of ridges also suggest the additional effect of transverse winds that create blow outs, while changes in the ridge packages planview onlap suggest possible changes in the dominant longshore drift. Four OSL samples located strategically allow defining the age of five main stages of this succession. The first stage comprises 2 substages. The first substage shows ridges #1 to #36 onlapping the boundary coastal scarp northwardly, while the second (ridges #37 to #84) shows an inversion of ridge shape wedging out southwards until coast returns to be quasi parallel to the initial coastal scarp estimated to be c. 6 ka. We estimate this first stage to comprise enhanced coastal drift due to higher and sandier ridges, ending at c. 4.1 ka. The second stage (ridges #85 to #124) ridges is marked by a slight unconformity, and indicates a period of enhanced fluvial progradation and less coastal drift suggesting milder winds up to 3.6 ka. The third stage (ridges #125 to #204) initiates with erosion of ridges near the delta front, being higher and sandier ridges, suggesting enhanced coastal drift due to windier conditions, being the windiest time bracketed between 3.3 and 2.35 ka. The fourth stage (ridges #205 to c. #270) shows again, as second stage, a tendency of wedging out southwards, suggesting enhanced fluvial progradation, estimated between 2.34 and 1.7 ka. The fifth stage is defined by a complete change of coastal plain progradation, due to the rapid recycling of beach ridges into a complex of blow outs and arcuate sand dunes. Ridges are sparsely recognized in cases they developed during short lived events of enhanced longshore drift, with an outstanding group (ridges #288 to #290) that we correlate to a 1.1–0.9 ka cooling event. Future studies, improving the chronostratigraphy of the beach ridges succession at Rio Grande and comparing it with the Parana river delta ridges, will help understanding the complex environmental history of South America, that include a reversal of the longshore drift, given the fact they are among the most complete upper Holocene geoarchives available.

Ecological divergence of Chaetopteryx rugulosa species complex (Insecta, Trichoptera) linked to climatic niche diversification

Climate is often considered to be an important, but indirect driver of speciation. Indeed, environmental factors may contribute to the formation of biodiversity, but to date this crucial relationship remains largely unexplored. Here we investigate the possible role of climate, geological factors, and biogeographical processes in the formation of a freshwater insect species group, the Chaetopteryx rugulosa species complex (Trichoptera) in the Western Balkans. We used multi-locus DNA sequence data to establish a dated phylogenetic hypothesis for the group. The comparison of the dated phylogeny with the geological history of the Western Balkans shows that lineage formation coincided with major past Earth surface and climatic events in the region. By reconstructing present-day habitat conditions (climate, bedrock geology), we show that the lineages of C. rugulosa species complex have distinct climatic but not bedrock geological niches. Without exception, all splits associated with Pliocene/Pleistocene transition led to independent, parallel split into ‘warm’ and ‘cold’ sister lineages. This indicates a non-random diversification on the C. rugulosa species complex associated with late Pliocene climate in the region. We interpreted the results as the diversification of the species complex were mainly driven by ecological diversification linked to past climate change, along with geographical isolation.

Lineage splitting, secondary contacts and genetic admixture of a widely distributed marine invertebrate

AbstractAimWe explore the genetic structure of the widespread starfish, Marthasterias spp., in order to: (1) identify historical causes of genetic divergence, (2) test the effect of past climatic events on populations’ demography and (3) explore main barriers to gene flow.LocationNorth‐ and south‐east Atlantic Ocean and Mediterranean Sea.MethodsWe amplified and sequenced three mitochondrial genes and one nuclear intron, and genotyped five nuclear microsatellite loci from 337 specimens. We reconstructed the phylogeny and phylogeography of Marthasterias spp. using the obtained DNA sequences, and used the microsatellite loci to explore major genetic discontinuities along the European coast.ResultsOur results suggested the existence of two allopatric species, one in the Northern Hemisphere (M. glacialis) and another in the Southern Hemisphere (Marthasterias sp.). This allopatric split could be attributed to recent changes in oceanographic circulation of the eastern Atlantic Ocean that may have acted as barrier to gene flow. Mitochondrial divergence between European lineages could be attributed to potential vicariance during Pleistocene glacial periods, but was not supported by nuclear markers, which may be indicative of recent genetic admixture. Secondary contact after glacial periods and gene flow across the Gibraltar Strait may explain this pattern. Genetic structure of M. glacialis based on nuclear markers did not show much divergence among geographical areas although most populations were significantly differentiated.Main conclusionsThe phylogeography of the widely distributed genus Marthasterias has most likely been shaped by recent changes in climate and oceanographic patterns. Major changes of ocean current patterns initially resulted in splitting between Northern and Southern Hemisphere lineages. Subsequently, glacial periods most likely enhanced vicariance of European lineages, followed by a post‐glacial expansion facilitating secondary contacts and genetic admixture.

Genetic and morphological variation in an ecosystem engineer, Lithophyllum byssoides (Corallinales, Rhodophyta).

Lithophyllum byssoides is a common coralline alga in the intertidal zone of Mediterranean coasts, where it produces biogenic concretions housing a high algal and invertebrate biodiversity. This species is an ecosystem engineer and is considered a target for conservation efforts, but designing effective conservation strategies currently is impossible due to lack of information about its population structure. The morphological and molecular variation of L.byssoides was investigated using morphoanatomy and DNA sequences (psbA and cox2,3) obtained from populations at 15 localities on the Italian and Croatian coasts. Lithophyllumbyssoides exhibited a high number of haplotypes (31 psbA haplotypes and 24 cox2,3 haplotypes) in the central Mediterranean. The psbA and cox2,3 phylogenies were congruent and showed seven lineages. For most of these clades, the distribution was limited to one or a few localities, but one of them (clade 7) was widespread across the central Mediterranean, spanning the main biogeographic boundaries recognized in this area. The central Mediterranean populations formed a lineage separate from Atlantic samples; psbA pair-wise divergences suggested that recognition of Atlantic and Mediterranean L.byssoides as different species may be appropriate. The central Mediterranean haplotype patterns of L.byssoides were interpreted as resulting from past climatic events in the hydrogeological history of the Mediterranean Sea. The high haplotype diversity and the restricted spatial distribution of the seven lineages suggest that individual populations should be managed as independent units.

Holocene eolian sand deposition linked to climatic variability, Northern Great Plains, Canada

The Bigstick and Seward Sand Hills are possibly two of the oldest dune fields within the late Wisconsin glaciated regions of the Northern Great Plains. As with most Northern Great Plains dune fields, source sediments are former proglacial outwash sands. Thus, Holocene dune construction is primarily related to spatial–temporal variations in surface cover and transport capacity, rather than renewed sediment input. However, eolian landscape reconstructions on the Northern Great Plains have been temporally constrained to recent periods of activity, as older episodes of deposition are typically reworked by younger events. In this study, sediment cores from shallow lacustrine basins and interdune areas provide an improved record of Holocene eolian sand deposition. Eolian sand accumulation in the interdunes and basins occurred between 150 and 270 years ago, 1.9 and 3.0 ka, 5.4 and 8.6 ka, and prior to ca. 10.8 ka. These episodes of sand accumulation were bracketed by lacustrine deposition and soil formation, which represented wetter conditions. Other than mid-Holocene dune activity, which may be related to peak warmth and aridity, most periods of eolian sand accumulation coincided with cooler but drier climatic events such as the Younger Dryas, late-Holocene cooling prior to the Medieval Climatic Anomaly, and the ‘Little Ice Age’. These depositional episodes are also spatially represented by other dune fields in the region, providing a broad-scale view of the connections between past climatic events and eolian landscape evolution on the Northern Great Plains.

Low genetic diversity and recent demographic expansion in the red starfish Echinaster sepositus (Retzius 1816).

Understanding the phylogeography and genetic structure of populations and the processes responsible of patterns therein is crucial for evaluating the vulnerability of marine species and developing management strategies. In this study, we explore how past climatic events and ongoing oceanographic and demographic processes have shaped the genetic structure and diversity of the Atlanto-Mediterranean red starfish Echinaster sepositus. The species is relatively abundant in some areas of the Mediterranean Sea, but some populations have dramatically decreased over recent years due to direct extraction for ornamental aquariums and souvenir industries. Analyses across most of the distribution range of the species based on the mitochondrial cytochrome c oxidase subunit I gene and eight microsatellite loci revealed very low intraspecific genetic diversity. The species showed a weak genetic structure within marine basins despite the a priori low dispersal potential of its lecithotrophic larva. Our results also revealed a very recent demographic expansion across the distribution range of the species. The genetic data presented here indicate that the species might be highly vulnerable, due to its low intraspecific genetic diversity.

Old Lineage on an Old Island: Pixibinthus, a New Cricket Genus Endemic to New Caledonia Shed Light on Gryllid Diversification in a Hotspot of Biodiversity.

Few studies have focused on the early colonization of New Caledonia by insects, after the re-emergence of the main island, 37 Myr ago. Here we investigate the mode and tempo of evolution of a new endemic cricket genus, Pixibinthus, recently discovered in southern New Caledonia. First we formally describe this new monotypic genus found exclusively in the open shrubby vegetation on metalliferous soils, named ‘maquis minier’, unique to New Caledonia. We then reconstruct a dated molecular phylogeny based on five mitochondrial and four nuclear loci in order to establish relationships of Pixibinthus within Eneopterinae crickets. Pixibinthus is recovered as thesister clade of the endemic genus Agnotecous, mostly rainforest-dwellers. Dating results show that the island colonization by their common ancestor occurred around 34.7 Myr, shortly after New Caledonia re-emergence. Pixibinthus and Agnotecous are then one of the oldest insect lineages documented so far for New Caledonia. This discovery highlights for the first time two clear-cut ecological specializations between sister clades, as Agnotecous is mainly found in rainforests with 19 species, whereas Pixibinthus is found in open habitats with a single documented species. The preference of Pixibinthus for open habitats and of Agnotecous for forest habitats nicely fits an acoustic specialization, either explained by differences in body size or in acoustic properties of their respective habitats. We hypothesize that landscape dynamics, linked to major past climatic events and recent change in fire regimes are possible causes for both present-day low diversity and rarity in genus Pixibinthus. The unique evolutionary history of this old New Caledonian lineage stresses the importance to increase our knowledge on the faunal biodiversity of ‘maquis minier’, in order to better understand the origin and past dynamics of New Caledonian biota.

Mollusks: Tools in Environmental and Climate Research*

Abstract: Mollusks are among the most diverse and abundant animal groups, inhabiting many aquatic and terrestrial environments. They are important ecosystem engineers, helping to structure aquatic bottom environments and providing habitat, protection, and food to a wide array of other taxa. Mollusks have been historically important to humans in many ways, and are today an economically important group worldwide. As major calcareous organisms with an extensive fossil record, they can provide important information on past climate events and oceanic changes, thus, increasing our understanding of predicted future changes. This paper presents an overview of the use of mollusks in environmental and impact studies, to provide a baseline towards a wider use of this diverse group ( and the valuable collections housed in many museums) as proxies in environmental reconstruction, climate change, ocean warming, and acidification research.

The age of the Hengelo interstadial revisited

Understanding past climate events relies for a large part on correlations between various proxy records. For the last glacial cycle, these are mainly marine and ice core records. However, such tele-connections are often based on weak arguments. For terrestrial data the Hengelo interstadial is a key event, discovered more than 4 decades ago. Here we review the age of this event, in particular by its 14C dates, their calibration and comparison with other proxy records. We conclude that the Hengelo interstadial, at the type locality and a few nearby comparable sites, dates between 36,000 and 38,600 BP (uncalibrated radiocarbon age), corresponding to 42,350 and 41,380 calBP. Correlation of the Hengelo interstadial with ice-core records remains problematic.

Marine tephra in the Japan Sea sediments as a tool for paleoceanography and paleoclimatology

Tephra is a product of large and explosive volcanic events and can travel thousands of kilometers before deposition. Consequently, tephra deposits are common in terrestrial, lacustrine, marine, and glacial environments. Because tephra deposition is a geologically synchronous event, tephras constitute important isochrones in the Quaternary sequence, not only in Japan but also throughout the northwest Pacific and its marginal seas. As a result, establishing the chronostratigraphic order of tephra deposits is an effective tool for assessing local and regional stratigraphies and for correlating events among sites. For example, tephrostratigraphy can provide precise chronological constraints for other stratigraphic data, such as magneto- and biostratigraphic data. Spatiotemporal variability in the occurrence and geochemistry of tephras can also be used to trace the magmatic evolution of island arcs and their relationships to regional tectonics. In a paleoclimatic context, tephra deposits allow the correlation of past climate events among terrestrial, lacustrine, and marine environments. Tephrochronology is also a fundamental element used in reconstructing the marine reservoir effect, where the ages of tephra in marine and terrestrial settings are compared. Therefore, tephra is a valuable tool not only in stratigraphy, chronology, and volcanology but also in paleoceanography and paleoclimatology.

Climatology in support of climate risk management

Climate risk management has emerged over the last decade as a distinct area of activity within the wider field of climatology. Its focus is on integrating climate and non-climate information in order to enhance the decision-making process in a wide range of climate-sensitive sectors of society, the economy and the environment. Given the burgeoning pure and applied climate science literature that addresses a range of climate risks, the purpose of this progress report is to provide an overview of recent developments in the field of climatology that may contribute to the risk assessment component of climate risk management. Data rescue and climate database construction, hurricanes and droughts as examples of extreme climate events and seasonal climate forecasting are focused on in this report and are privileged over other topics because of either their fundamental importance for establishing event probability or scale of societal impact. The review of the literature finds that historical data rescue, climate reconstruction and the compilation of climate data bases has assisted immensely in understanding past climate events and increasing the information base for managing climate risk. Advances in the scientific understanding of the causes and the characterization of hurricanes and droughts stand to benefit the management of these two extreme events while work focused on unravelling the nature of ocean–atmosphere interactions and associated climate anomalies at the seasonal timescale has provided the basis for the possible seasonal forecasting of a range of climate events. The report also acknowledges that despite the potential of climate information to assist with managing climate risk, its uptake by decision makers should not be automatically assumed by the climatological community.

The C20 highly branched isoprenoid biomarker – A new diatom-sourced proxy for summer trophic conditions?

The exact biological source of the C20 highly branched isoprenoid (HBI) present in sediments from aquatic systems is unclear. We therefore examined the relationship between the distribution of fossil diatoms and the concentration of the C20 HBI in a Late Glacial sedimentary record from the Hässeldala Port paleolake in southern Sweden. Using Bayesian multiple linear regression analysis, we show that its concentration is linked primarily to the production of the diatom taxon Gomphonema acuminatum, which accounts for the largest proportion of the temporal variability in the biomarker. By analogy with modern observations, we argue that an increasing amount of G. acuminatum biomass in our sedimentary record reflects increasing oligotrophy in the paleolake during the summer growing season, especially at times defined by subdued hydrologic flow. Our conclusions are corroborated by the δ13C composition of the C20 HBI biomarker, which points to a negative photosynthetic fractionation between atmospheric CO2 and the pool of dissolved inorganic carbon during diatom bloom, a distinct phenomenon at times of inhibited hydrological flow. Accordingly, we suggest that the C20 HBI biomarker can be effectively used to reconstruct the trophic state of the paleolake at Hässeldala Port, while its stable isotope composition can provide physicochemical information about the lake conditions during the dry summer season.Moreover, we note that the major hydrological shifts recorded in the G. acuminatum-C20 HBI stratigraphy do not coincide with the pollen zone boundaries. We thus infer that aquatic and terrestrial environmental responses to climate change are substantially decoupled through the hydrological system, which highlights the necessity for multi-proxy investigations to decipher past climate events.