Roman Warm Period Research Articles

Fluvial response to rising levels of the Black Sea and to climate changes during the Holocene: Luminescence geochronology of the Sakarya terraces

The Sakarya River is among the largest fluvial systems of the southern Black Sea basin, draining most of NW Anatolia. The river crosses the high relief of the Pontide mountain range through successive narrow gorges and strike-slip basins formed by the North Anatolian Fault (NAF) System. We have investigated this fluvial record along the course of the main river channel at its lower reaches. The study site is located south of the Adapazarı Basin, ~50 km inland from the Black Sea, where remnant floodplains are preserved as a three-step terrace staircase resulting from continuous uplift to the south of the NAF. The combination of high resolution mapping with a detailed luminescence (OSL and p-IR-IRSL) and radiocarbon geochronology has shed light on changes in the level of the Black Sea and in the hydrological system during the late Pleistocene to recent. The last glacial period is represented by the highest terrace (T3) indicating deposition during marine isotope stage (MIS) 3 in between two low stands of the Black Sea. Following a long-term erosional period initiated prior to last glacial maximum (LGM), the initiation of the deposition (T2) was synchronous with the proposed catastrophic sea level rise of the Black Sea (cal. C14 9.3 ka BP) which continued throughout the Holocene until the Roman warm period (1.8 ka BP). The late-Holocene to recent morphological evolution of the region is marked with two sequential erosional and depositional (T1 and T0) periods, which can be correlated with the well-documented historical climate shifts affecting the hydrological system. These results reveal that the erosional and depositional periods on the Sakarya River floodplain are controlled by major sea level changes and climatically induced fluctuations in discharge and sediment supply.

Late Holocene vegetation, climate, and natural disturbance records from an alpine pond in central Taiwan

Paleo-typhoon activity and its correlation with El Niño Southern Oscillation (ENSO) during the late Holocene has been reported by numerous studies, but our understanding of the impacts of typhoons as natural disturbance events on subtropical forest ecosystems remains unclear. In this study, we used a multi-proxy method, including pollen, grain size, and the ratios of Sr/Ti and Rb/Ti from XRF-scanning measurements, on a sediment core from Tunlumei Pond (TLM) to reconstruct vegetation dynamics and the records of natural disturbances, such as heavy rainfalls, earthquakes, or typhoons, in central alpine Taiwan during the past 2400 calibrated years before the present (cal yr BP, where “present” refers to 1950 AD). The trend in variation between the percentages of upper montane forests and PC1 value indicates that the cold/dry climate changed to a warm/humid climate from 1800 cal yr BP upward, corresponding to the Roman Warm Period. This local change might be corresponded to regional trend and relative to the East Asian summer monsoon fluctuation. Coarse grain particles associated with the transition of the pollen zone indicate frequent and/or strong natural disturbances at 1510 cal yr BP and the impacts of the early Little Ice Age (LIA) during 530–480 cal yr BP. The palaeoecological record of TLM provides very useful information for both decision making and policy planning in present and future subtropical forest management, as well as restoration after a catastrophic event.

Signatures of global climatic events and forcing factors for the last two millennia from the active mudflats of Rohisa, southern Saurashtra, Gujarat, western India

The limited extent of instrumental records going back in time and control of various climatic variables on Indian Summer Monsoon (ISM) has reinvigorated the unprecedented effort in documenting climate changes for the last two millennia. Although extensive studies on late Holocene ISM reconstruction are available, comprehensive understanding on the influence of natural forcing factors on ISM and their plausible signatures is not arrived at till date. In view of this, the present study attempts to address the ISM variations during the last two millennia with special emphasis on natural forcing factors (solar and volcanic) and climate variables (ocean-atmospheric processes). The Saurashtra peninsula of Gujarat in western India receives majority of rainfall during ISM and hence it provides an ideal test-bed to study the ISM variability. A multiproxy approach has been adopted on a sediment core retrieved from the active mudflat of Southern Saurashtra which was chronologically supported by 210Pb, 137Cs and 14C. The present study demonstrates vacillating climate with strengthened ISM during Roman Warm Period and Medieval Warm Period (2000−950 cal yr BP) as a result of increased solar irradiance interrupted by reduced ISM during Dark Ages of Cold Period (∼1500 cal yr BP). The plausible occurrence of volcanic eruption before the onset of Little Ice Age (500−200 cal yr BP) caused the southward migration of Intertropical Convergence Zone (ITCZ) leading to enhanced western disturbances in the study area thereby resulting in cool and wet climate in the region. The study also emphasizes the increased El Nino events with gradual decline in the ISM since Little Ice Age. Further, the study underscores a climate warming during the last two centuries that corroborates well with the instrumental records. Thus, the present study has implication towards understanding the significant role of volcanic activity and solar variability in controlling the millennia scale climate oscillations with additional feedback mechanisms.

Late Holocene palaeo-environmental change in the Banni Plains, Kachchh, Western India

The effect of the environmental change during the Middle to Late Holocene period, on the demise of the mighty Harappan civilization has remained a topic of debate. The western India, especially the coastal regions, hosted a cluster of Harappan settlements near the shoreline. The present study attempts to reconstruct the evolution of Banni Plains of the Kachchh region, which has remained a hotspot for Harappan civilization. We employed a host of multi-proxy techniques viz., sedimentology, sediment geochemistry, magnetic susceptibility along with OSL chronology, to deduce the palaeo-environmental changes experienced by the Banni Plains from a shallow 4.05 m deep trench. The four OSL chronology of the sediments suggests the time span of 2.9 ka to 0.2 ka, revealing a first hand estimate of average sedimentation rate of 1.5 mm per annum. The enhanced chemical weathering intensities suggest that the last two millennia witnessed two phases of relatively warm and humid climatic conditions, which probably coincide with the Roman Warm Period (?) and the Medieval Warm Period (?). The Banni Plains was evolved owing to the Middle Holocene high sea stand and subsequent relative fall during the last 2 ka period. The extent of the relative high sea stand upto 2 m above msl also corroborated well by ancient port settlements of the Late Harappan period. This implies that the Harappan civilization was indeed influenced and affected by the past sea level change; nevertheless, this cannot be the sole reason for demise of the mighty civilization, but remained an auxiliary mechanism along with aridity which severed the human adaptation.

Late-Holocene high-frequency East Asia Winter Monsoon variability inferred from the environmentally sensitive grain size component in the distal shelf mud area, East China Sea

The B2 (B2G) and I4 sediment cores recovered from the centre of the distal mud area of the East China Sea (ECS) were analysed for grain size distribution. Proxies for environmentally sensitive grain size components (ESGSC) retrieved from the composite B2 core, namely, variations in the volumetric content and mean grain size of specific grain size fractions, reveal a detailed history of the East Asia Winter Monsoon (EAWM) including centennial to decadal-scale variations spanning the last 2300 calendar years before present (cal. yr BP). The results indicate that EAWM variations are consistent with temperature changes in eastern China (as inferred from historical documents). Additionally, the sea surface temperature (SST) in the Southern Okinawa Trough, the δ18O of stalagmite from the Sanbao cave and the drift ice indices from the North Atlantic, along with strong or weak EAWMs, corresponding to low or high temperatures, respectively. Four periods of EAWM variations were identified, namely, a weak EAWM stage from 2300 to 2050 cal. yr BP; a comparatively enhanced EAWM between 2050 and 1700 cal. yr BP; a return to a weak EAWM from 1700 to 700 cal. yr BP, including the Roman Warm Period (RWP), the Sui–Tang Dynasty Warm Period (STWP) and the ‘Medieval Warm Period’ (MWP) and a strongly developed EAWM between 700 and 100 cal. yr BP, corresponding to a ‘Little Ice Age’. An important abrupt warm to cold climate change event occurred around 678 cal. yr BP. During this period, the climate change was likely related to global scale changes in atmospheric circulation. Spectral analyses of the ESGSC proxies show high-frequency cycles and a close solar–monsoon connection to the EAWM, suggesting that one of the primary controls for centennial to decadal-scale change in EAWM intensity was the variation in solar radiation during that time.

Holocene climatic conditions in the eastern Adriatic recorded in stalagmites from Strašna peć Cave (Croatia)

In the study we present results of stable isotope analysis (δ18O, δ13C) of two stalagmites (SPD-1 and SPD-2) from Strašna peć Cave, situated on Dugi otok Island in the Central Adriatic region. The growth interval of the speleothems based on U-Th dating covers the period from 4.4 ka to 1.5 ka. Both speleothems show frequent δ18O and δ13C fluctuations with similar average values (δ18O value of -4‰ for both speleothems; and average value of δ13C-8.5‰ and −8.8‰, respectively). In order to reconstruct the Holocene climatic conditions in the Eastern Adriatic, the speleothem isotopic record is discussed and compared with other Holocene records. They reveal periods of drought which occurred at 4.3–4 ka and around 3.5 ka, with relatively wet phases between. From 3 ka, there is a general trend towards dryness as evidentiated by the relatively high δ18O values of -3.5‰ to -2.5‰ recorded in speleothem SPD-1. There is distinct trend of drying during the Roman Warm Period and further toward the Dark Age Cold Period (DACP) with shorter periods of wetter conditions. These changes coincide well with the other records, thus revealing regional events along the Eastern Adriatic.

Peat δ13Ccelluose-signified moisture variations over the past ∼2200 years in the southern Altai Mountains, northwestern China

A ∼2200-year moisture history of the southern Altai Mountains (i.e., Chinese Altai) was established based on peat δ13Ccelluose data obtained at Yushenkule (YSKL) Peat. Generally speaking, the moisture record from YSKL Peat exhibits a “cool-wet” DACP (Dark Age Cold Period from ∼500 to ∼800 CE), a “warm-dry” MWP (Medieval Warm Period from ∼800 to ∼1200 CE), a “cool-wet” LIA (Little Ice Age from ∼1200 to ∼1900 CE), and a “warm-dry” CWP (Current Warm Period since ∼1900 CE). But, RWP (Roman Warm Period from prior to ∼100 CE to ∼500 CE) is an exception (i.e., “warm-wet”). If the heat-water combinations within those major temperature-change events are further examined, the “warm-dry/cool-wet” generalization collapses. The comparisons between the variations in the peat δ13Ccelluose-based moisture obtained from YSKL Peat and the variations of reconstructed climatic variables in the referenced sequences suggest that the moisture variations in the Altai Mountains have been basically controlled by the precipitation that was primarily modulated by the NAO variations.

Burning-derived vanillic acid in an Arctic ice core from Tunu, northeastern Greenland

Abstract. In this study, vanillic acid was measured in the Tunu ice core from northeastern Greenland in samples covering the past 1700 years. Vanillic acid is an aerosol-borne aromatic methoxy acid, produced by the combustion of lignin during biomass burning. Air mass trajectory analysis indicates that North American boreal forests are likely the major source region for biomass burning aerosols deposited to the ice core site. Vanillic acid levels in the Tunu ice core range from < 0.005 to 0.08 ppb. Tunu vanillic acid exhibits centennial-scale variability in pre-industrial ice, with elevated levels during the warm climates of the Roman Warm Period and Medieval Climate Anomaly, and lower levels during the cooler climates of the Late Antique Little Ice Age and the Little Ice Age. Analysis using a peak detection method revealed a positive correlation between vanillic acid in the Tunu ice core and both ammonium and black carbon in the North Greenland Eemian Ice Drilling (NEEM) project ice core from 600 to 1200 CE. The data provide multiproxy evidence of centennial-scale variability in North American high-latitude fire during this time period.

Response of lake-catchment processes to Holocene climate variability: Evidences from the NE Tibetan Plateau

Investigating the so-called Third Pole Environment (TPE) became a major concern during the last decades since it was recognized that the high-altitude region of the Tibetan Plateau (TP) is a key area for the understanding of cause-effect mechanisms driven by climate change and geodynamic processes. Studies on the hydro-climatic evolution during the Late Quaternary were mainly carried out by single lake records or alternatively by individual terrestrial sites. Integrated source-to sink studies considering lake–catchment interactions were extremely seldom utilized. We investigated such relationships in the Kuhai Basin on the north-eastern Tibetan Plateau and analysed sedimentary processes based on 30 onshore sections and three sediment cores from different locations and water depth in the lake basin. Grain size variations, ostracod assemblages, geochemical proxies and absolute dating (luminescence, radiocarbon, 210Pb/137Cs) were applied as key indicators that reveal interacting sediment fluxes under different hydro-climatic settings during the Younger Dryas interval and the Holocene. Our results indicate that wind-induced transportation processes and allocation of respective aeolian sands in the catchment are attributed to distinct phases of reduced effective moisture availability during summer time. Those phases corresponded to weak summer monsoon influence during the Younger Dryas interval, the Early Holocene (11.6–7.5 ka), dry-cold interlude (DCI: ca. 4.5–3.0 ka), Dark Ages Cold Period (DACP: ca. 1.8–1.1 ka) and the Little Ice Age (LIA: ca. 0.6–0.1 ka). Contemporaneous low lake levels during these periods corresponded with respective aeolian sand flux and variable composition of mixed sediments (fluvial and aeolian) in lake deposits. Different flux rates at the core sites could be assigned to local conditions in respect to inflow behaviour of individual drainage systems and nearshore morphology. Aeolian deposits in the catchment were not always preserved and underwent re-mobilisation during succeeding episodes and/or erosion during phases of high water availability. Wetter climatic conditions during the Mid-Holocene (ca. 7.5–5.1 ka), Roman Warm Period (RWP: ca. 2.8–1.5 ka) and Medieval Climate Anomaly (MCA: ca. 0.9–0.6 ka) revealed significant lake level rise due to enhanced river discharge, well documented by highest suspended flux rates, disappearance of ostracod communities at core sites and very low sand input. Climate shifts during the Holocene were linked to variations in effective moisture supply under the influence of the Asian summer monsoon (ASM) and the interplay with the mid-latitude westerlies (MLW). Cold-dry phases were likely a response to North Atlantic climatic anomalies transmitted by the MLW across the TP.

Tracing winter temperatures over the last two millennia using a north-east Atlantic coastal record

Abstract. We present 2500 years of reconstructed bottom water temperatures (BWT) using a fjord sediment archive from the north-east Atlantic region. The BWT represent winter conditions due to the fjord hydrography and the associated timing and frequency of bottom water renewals. The study is based on a ca. 8 m long sediment core from Gullmar Fjord (Sweden), which was dated by 210Pb and AMS 14C and analysed for stable oxygen isotopes (δ18O) measured on shallow infaunal benthic foraminiferal species Cassidulina laevigata d'Orbigny 1826. The BWT, calculated using the palaeotemperature equation from McCorkle et al. (1997), range between 2.7 and 7.8 ∘C and are within the annual temperature variability that has been instrumentally recorded in the deep fjord basin since the 1890s. The record demonstrates a warming during the Roman Warm Period (∼350 BCE–450 CE), variable BWT during the Dark Ages (∼450–850 CE), positive BWT anomalies during the Viking Age/Medieval Climate Anomaly (∼850–1350 CE) and a long-term cooling with distinct multidecadal variability during the Little Ice Age (∼1350–1850 CE). The fjord BWT record also picks up the contemporary warming of the 20th century (presented here until 1996), which does not stand out in the 2500-year perspective and is of the same magnitude as the Roman Warm Period and the Medieval Climate Anomaly.

Timing of rockfalls in the Mont Blanc massif (Western Alps): evidence from surface exposure dating with cosmogenic 10Be

Rockfalls and rock avalanches are a recurrent process in high mountain areas like the Mont Blanc massif. These processes are surveyed due to the hazard they present for infrastructure and alpinists. While rockfalls and rock avalanches have been documented for the last 150 years, we know very little about their frequency since the Last Glacial Maximum (LGM). In order to improve our understanding, it is imperative to date them on a longer timescale. A pilot campaign using Terrestrial Cosmogenic Nuclide (TCN) dating of five samples was carried out in 2006 at the Aiguille du Midi (3842 m a.s.l.). In 2011, a larger scale study (20 samples) was carried out in five other test sites in the Mont Blanc massif. This paper presents the exposure ages of the 2011 TCN study as well as the updated exposure ages of the 2006 study using newer TCN dating parameters. Most of these exposure ages lie within the Holocene but three ages are Pleistocene (59.87 ± 6.10 ka for the oldest). A comparison of these ages with air temperature and glacier cover proxies explored the possible relationship between the most active rockfall periods and the warmest periods of the Holocene: two clusters of exposure ages have been detected, corresponding to the Middle Holocene (8.2–4.2 ka) and the Roman Warm Period (c. 2 ka) climate periods. Some recent rockfalls have also been dated (< 0.56 ka).

Global warming in the context of 2000 years of Australian alpine temperature and snow cover

Annual resolution reconstructions of alpine temperatures are rare, particularly for the Southern Hemisphere, while no snow cover reconstructions exist. These records are essential to place in context the impact of anthropogenic global warming against historical major natural climate events such as the Roman Warm Period (RWP), Medieval Climate Anomaly (MCA) and Little Ice Age (LIA). Here we show for a marginal alpine region of Australia using a carbon isotope speleothem reconstruction, warming over the past five decades has experienced equivalent magnitude of temperature change and snow cover decline to the RWP and MCA. The current rate of warming is unmatched for the past 2000 years and seasonal snow cover is at a minimum. On scales of several decades, mean maximum temperatures have undergone considerable change ≈ ± 0.8 °C highlighting local scale susceptibility to rapid temperature change, evidence of which is often masked in regional to hemisphere scale temperature reconstructions.

Late Holocene high resolution multi-proxy climate and environmental records from Lake Van, eastern Turkey

We present the multi-proxy records of centennial scale climate and environmental changes over the last 3.5 ka from a varved sediment core in Lake Van, eastern Turkey. The multi-proxy analyses include ostracod counts, μ-XRF elemental, total organic (TOC) and inorganic carbon, C-N elemental and stable isotopes. For the age model of the core, we use radionuclide (210Pb and 137Cs) analysis and varve counting. Large differences between Accelerator Mass Spectrometry (AMS) radiocarbon dates from TOC and varve ages indicate reservoir ages of 1.2–3.8 ka calBP. Average sedimentation rate for the last 170 years (top 75 mm of the core) ranges between 0.42 and 0.54 mm/yr according to 210Pb dating.Multi-proxy parameters show that Lake Van experienced more arid conditions during the 3.5–1.6 Ka calBP than those during the last 1.6 ka BP. 16 periods of alternating cold/dry and warm/wet intervals with 100–350 years duration are observed over the last 3.5 ka. The Lake Van climate records are conformable with the Lake Nar and the Sofular speleothem records as well as the European historical climate periods including Roman Warm Period (RWP), Dark Age Cold Period (DACP), Medieval Warm Period (MWP) and Little Ice Age (LIA), indicating teleconnections with the North Atlantic system. Human influence is reflected by high detrital influx in the last 700 years.

Subfossil markers of climate change during the Roman Warm Period of the late Holocene.

Abundant bog oak trunks occur in alluvial deposits of the Raba River in the village of Targowisko (southern Poland). Several of them contain galleries of the great capricorn beetle (Cerambyx cerdo L.). A well-preserved subfossil larva and pupa, as well as adults of this species, are concealed in some of the galleries. These galleries co-occur with boring galleries of other insects such as ship-timber beetles (Lymexylidae) and metallic wood borers (Buprestidae). A dry larva of a stag beetle (Lucanidae) and a mite (Acari) have been found in the C. cerdo galleries. Selected samples of the trunks and a sample of the C. cerdo larva were dated, using radiocarbon and dendrochronological methods, to the period from 45BC to AD 554; one sample was dated to the period from 799 to 700BC. Accumulation of the channel alluvia containing the bog oak trunks is synchronous with the Roman Warm Period (late antiquity/Early Mediaeval times). The most recent part of this period correlates with massive accumulations of fallen oak trunks noted from various river valleys in the Carpathian region and dated to AD 450-570. The results indicate that C. cerdo was more abundant within the study area during the Roman Warm Period than it is today.

Heat export from the tropics drives mid to late Holocene palaeoceanographic changes offshore southern Australia

The Leeuwin Current (LC), an eastern boundary current, transports tropical waters from the Indo-Pacific Warm Pool (IPWP) towards southern latitudes and modulates oceanic conditions offshore southern Australia. New, high-resolution planktic foraminifer assemblage data and alkenone-derived sea surface temperatures (SST) provide an in-depth view on LC variability and mechanisms driving the current's properties during the mid to late Holocene (last c. 7.4 ka BP). Our marine reconstructions highlight a longer-term mid to late Holocene reduction of tropical heat export from the IPWP area into the LC. Mid Holocene (c. 7.4 to 3.5 ka BP) occurrence of high SSTs (>19.5 °C), tropical planktic foraminifera and a well-stratified water column document an enhanced heat export from the tropics. From c. 3.5 ka BP onwards, a weaker LC and a notably reduced tropical heat export cause oceanic cooling offshore southern Australia. The observed mid to late Holocene trends likely result from large-scale changes in the IPWP's heat storage linked to the El Niño-Southern Oscillation (ENSO) phenomenon. We propose that a strong and warm LC occurs in response to a La Niña-like state of ENSO during the mid Holocene. The late Holocene LC cooling, however, results from a shift towards an El Niño-like state and a more variable ENSO system that causes cooling of the IPWP. Superimposed on these longer-term trends we find evidence of distinct late Holocene millennial-scale phases of enhanced El Niño/La Niña development, which appear synchronous with northern hemispheric climatic variability. Phases of dominant El Niño-like states occur parallel to North Atlantic cold phases: the ‘2800 years BP cooling event’, the ‘Dark Ages’ and the ‘Little Ice Age’, whereas the ‘Roman Warm Period’ and the ‘Medieval Climate Anomaly’ parallel periods of a predominant La Niña-like state. Our findings provide further evidence of coherent interhemispheric climatic and oceanic conditions during the mid to late Holocene, suggesting ENSO as a potential mediator.

Paleoenvironmental reconstruction of an urban archaeological site: The Roman Salt mines of Vigo, northwest Iberia

AbstractPedostratigraphy applied to urban archaeological coastal sites, combined with coastal geomorphological and archaeological data, provide important information for interpreting the complexity of coastal urban areas and their environment. This paper applies this methodology in the case of the Roman salt mines of Vigo, northwest Spain, and presents geomorphological and geoarchaeological data (stratigraphy, physicochemical soil properties, mineralogy, radiocarbon dating) for the museum where these remains are located. A 2000 year pedostratigraphic sequence was reconstructed, showing coastal evolution from beach to marshland. This change, along with more favorable climatic conditions related to the Roman Warm Period and dynamics associated with late Holocene rising sea level, created suitable conditions for the establishment of a salt mine. Geoarchaeological work is essential in archaeological excavations of modern urban areas, as demonstrated at Vigo where the study of pedostratigraphy provides crucial information on past environmental changes and human activities. Pedostratigraphic records and archaeological remains should be considered part of the geological and cultural heritage of urban areas.

Variations in precipitation in North America during the past 2000 years

We present a 2000-year pollen-based reconstruction of total annual precipitation (ANNP) for North America. Application of Local Indices of Spatial Association (LISA) permitted us to distinguish regional large-scale hydroclimate patterns from local site-specific conditions across North America during this time period. Century-scale filtered pollen-based reconstructions are more spatially coherent than unfiltered reconstructions, allowing for better identification of past hydroclimate patterns across North America. Similar spatial patterns dominated during both the ‘Medieval Warm Period’ (MWP; 950–1250 CE) and Roman Warm Period (RWP; 50 BCE–150 CE), although the MWP was generally drier than the RWP. In contrast, hydroclimate changes during Dark Ages Cold Period (DAC; 350–650 CE) and the ‘Little Ice Age’ (LIA; 1550–1850 CE) show opposing patterns across the western and eastern boreal region of North America. During warm periods, eastern and western boreal regions had similar moisture condition, whereas during cold periods, the eastern boreal region was relatively wet and the west was dry.

A 5500-year oxygen isotope record of high arctic environmental change from southern Spitsbergen

The oxygen isotope composition of chironomid head capsules in a sediment core spanning the past 5500 years from Lake Svartvatnet in southern Spitsbergen was used to reconstruct the oxygen isotope composition of lake water (δ18Olw) and local precipitation. The δ18Olw values display shifts from the baseline variability consistent with the timing of recognized historical climatic episodes, such as the Roman Warm Period, the Dark Ages Cold Period and the ‘Little Ice Age’. The highest values of the record, ca. 3‰ above modern δ18Olw values, occur at ca. 1900–1800 cal. yr BP. Three negative excursions increasing in intensity toward the present, at 3400–3200, 1250–1100, and 350–50 cal. yr BP, are tentatively linked to roughly synchronous episodes of increased glacier activity and general cold spells around the northern North Atlantic. Their manifestation in the Svartvatnet δ18Olw record not only testify to the sensitivity and potential of high Arctic lacustrine δ18Ochir records in tracking terrestrial climate evolution but also highlight nonlinear dynamics within the northern North Atlantic hydroclimatic system. The ‘Little Ice Age’ period at 350–50 cal. yr BP displays a remarkable 8–9‰ drop in δ18Olw values, construed to predominantly represent significantly decreased winter temperatures during a period of increased seasonal differences and extended sea ice cover inducing changes in moisture source regions.

Reinforcing a Double Dynamo Model with Solar-Terrestrial Activity in the Past Three Millennia

AbstractBy applying Principal Components Analysis (PCA) to solar magnetic synoptic maps in cycle 21-23 obtained with Wilcox Solar Observatory we derived analytical expressions for two principal components and their summary curve of solar magnetic field oscillations defined by dipole magnetic sources. In this paper we extrapolate backwards three millennia the summary curve describing solar activity and compare it with the relevant historic data. The extrapolated summary curve shows a remarkable resemblance to the sunspot and terrestrial activity reported in the past millennia: the Maunder Minimum (1645-1715), Wolf minimum (1200), Oort minimum (1010-1050), Homer minimum (800-900 BC), the medieval warm period (900-1200), the Roman warm period (400-10BC). We note that Sporer minimum (1460-1550) derived from the increased abundance of isotope Δ14C is likely produced by a strong increase of galactic cosmic rays caused by a supernova Vela Junior occurred in the Southern hemisphere.

Short-term variability in late Holocene sea ice cover on the East Greenland Shelf and its driving mechanisms

Arctic sea ice is a critical component of the climate system as it influences the albedo, heat, moisture and gas exchange between ocean and atmosphere as well as the ocean's salinity. An ideal location to study natural sea ice variability during pre-industrial times is the East Greenland Shelf that underlies the East Greenland Current (EGC), the main route of Arctic sea ice and freshwaters from the Arctic Ocean into the northern North Atlantic. Here, we present a new high-resolution biomarker record from the East Greenland Shelf (73°N), which provides new insights into the sea ice variability and accompanying phytoplankton productivity over the past 5.2kyr. Our IP25 based sea ice reconstructions and the inferred PIP25 index do not reflect the wide-spread late Holocene Neoglacial cooling trend that follows the decreasing solar insolation pattern, which we relate to the strong influence of the polar EGC on the East Greenland Shelf and interactions with the adjacent fjord throughout the studied time interval. However, our reconstructions reveal several oscillations with increasing/decreasing sea ice concentrations that are linked to the known late Holocene climate cold/warm phases, i.e. the Roman Warm Period, Dark Ages Cold Period, Medieval Climate Anomaly and Little Ice Age. The observed changes seem to be connected to general ocean atmosphere circulation changes, possibly related to North Atlantic Oscillation and Atlantic Multidecadal Oscillation regimes. Furthermore, we identify a cyclicity of 73–74years in sea ice algae and phytoplankton productivity over the last 1.2kyr, which may indicate a connection to Atlantic Multidecadal Oscillation mechanisms.