Description: Publication date: 1 August 2018 Source: Quaternary Science Reviews, Volume 193 Author(s): H. Delile, J.P. Goiran, J. Blichert-Toft Once trapped in ancient harbor basins, sediments form environmental archives that have been widely studied by geoarcheologists in recent decades, especially to help reconstruct fluvio-marine landscapes of the last millennia. In some cases, classic environmental markers cannot be used for this purpose either because of their scarcity in the sedimentary deposits, or because analytical costs limit the resolution that can be achieved. In order to remedy these shortcomings, and to complement the more commonly used proxies, elemental and isotopic geochemistry has been added to the geoarcheological toolkit. Here we show how to “read” the evolution of the paleo-environmental dynamics in the water column of Ostia Antica (Rome's first maritime harbor) using the geochemical and isotopic record of a 3000-year-old sediment core drilled in the ancient harbor basin. A comparison of the results obtained from Ostia Antica with those of other ancient Mediterranean harbors reveals the nature of the main environmental processes operating during the formation of sedimentary deposits in harbor basins. From this comparative approach, it appears that the respective weight of each control factor is dependent on the coastal geomorphological context of the sites where the harbors were established. Since the discovery of the harbor of Ostia Antica in 2014, this method has provided the means, for the first time, to identify two distinct harbor basin regimes; an initial marine-dominated regime from the middle of the 4th c. BC to ∼ the 3rd c. BC, and a later freshwater-dominated regime up to the 2nd c. BC. More generally, we observe the effects of the dynamics of the deltaic progradation of the Tiber, which very early on was subject to a hydro-climatic component, on the processes of alluviation of the harbor basin. Additionally, and also for the first time in harbor geoarcheology, Pb isotope compositions measured specifically on uncontaminated sediments demonstrate their utility for both identifying the geological sources of the sediments of the Tiber delta and discriminating finer from larger particles. The present study further provides an opportunity to test the validity of two hypotheses recently put forward: (1) that a series of three tsunamis is recorded in the harbor silts, and (2) that an initial lagoon-type harbor was constructed at Ostia Antica, which later evolved into a fluvial harbor. Neither of these hypotheses are supported by the present data.

Description: Publication date: 15 August 2018 Source: Quaternary Science Reviews, Volume 194 Author(s): T. Elliott Arnold, Aaron F. Diefendorf, Mark Brenner, Katherine H. Freeman, Allison A. Baczynski Hydrogen and carbon isotope values (δD & δ 13 C) were measured on lipid biomarkers from a sediment core collected in Lake Tulane, Florida, USA, to infer shifts in climate and hydrologic variables during the Last Glacial. Isotopic trends from 24 samples correlate with plant community shifts evaluated in a previous pollen study by Grimm et al. (2006). We observe maxima in Δ leaf values and minima in δD values concurrent with peaks in Pinus pollen abundances and Heinrich Events 4-2. Increased Δ leaf values during North Atlantic cold spells indicate lower water-use-efficiency among angiosperms around Lake Tulane. Combined δD values from terrestrial and aquatic lipids, confirm that aridity decreased during cold, stadial periods (Heinrich Events), and increased during warm, interstadials. Furthermore, lower δD values in aquatic lipids during stadials are attributed to warming, as well as changing moisture sources. The anti-phase relationship between temperatures and aridity derived from our subtropical lacustrine record and those at high latitude in the North Atlantic is likely the result of complex ocean-atmosphere teleconnections that resulted from the collapse of Atlantic Meridional Overturning Circulation during Heinrich Events in the North Atlantic.

Description: Publication date: 1 August 2018 Source: Quaternary Science Reviews, Volume 193 Author(s): Christian Leipe, Stefanie Müller, Konrad Hille, Hirofumi Kato, Franziska Kobe, Mareike Schmidt, Konrad Seyffert, Robert Spengler, Mayke Wagner, Andrzej W. Weber, Pavel E. Tarasov This study presents a high-resolution, chronologically well-constrained pollen record from Lake Kushu (45°25′58″N, 141°02′05″E) and a record of archaeobotanical remains from the nearby Hamanaka 2 archaeological site. The pollen record suggests continuous long-term cooling, which parallels the decline in Northern Hemisphere summer insolation. This cooling trend is overlaid by several rather quick transitions towards cooler conditions (ca. 5540/5350, 1550, and 390 cal BP) and one distinct decadal-scale cold event around 4130 cal BP. These shifts, on one hand, correspond with major hemispherical or global-scale climate transitions/events, including the ‘Holocene Climate Transition’, the onset of the ‘Dark Ages Cold Period’ main phase, the ‘Little Ice Age’, and the ‘4.2 kiloyear event’, respectively. On the other hand, the shifts partly coincide with transformations in the Hokkaido prehistoric cultural sequence including the onset of the Middle Jomon (ca. 5000 cal BP), the Middle/Late Jomon transition (ca. 4000 cal BP), the immigration of Okhotsk culture groups (from ca. 1500 cal BP), and the establishment of the Classic Ainu culture (ca. 350 cal BP). AMS radiocarbon dating of charred macrobotanical remains from Hamanaka 2 suggests three discontinuous occupational periods ca. 390–50 BCE, 420–970 CE, and from 1640 CE, which correspond to the northern Hokkaido Epi Jomon (ca. 300–100 BCE), Okhotsk (ca. 500–1000 CE), and Classic Ainu (ca. 1600–1868 CE) cultural phases, respectively. While impact on the island's natural environments (forest clearance) was marginal during the Epi Jomon phase, it became significant during the Okhotsk and the Classic Ainu culture phases.

Description: Publication date: 1 August 2018 Source: Quaternary Science Reviews, Volume 193 Author(s): A.A. Bjørk, N.K. Larsen, J. Olsen, A.E. Goldsack, K.K. Kjeldsen, M. Morlighem, C.S. Andresen, P. Rasmussen, G. Oxfeldt, K.H. Kjær Helheim Glacier ranks among the fastest flowing and most ice discharging outlets of the Greenland Ice Sheet (GrIS). After undergoing rapid speed-up in the early 2000s, understanding its long-term mass balance and dynamic has become increasingly important. Here, we present the first record of direct Holocene ice-marginal changes of the Helheim Glacier following the initial deglaciation. By analysing cores from lakes adjacent to the present ice margin, we pinpoint periods of advance and retreat. We target threshold lakes, which receive glacial meltwater only when the margin is at an advanced position, similar to the present. We show that, during the period from 10.5 to 9.6 cal ka BP, the extent of Helheim Glacier was similar to that of todays, after which it remained retracted for most of the Holocene until a re-advance caused it to reach its present extent at c. 0.3 cal ka BP, during the Little Ice Age (LIA). Thus, Helheim Glacier's present extent is the largest since the last deglaciation, and its Holocene history shows that it is capable of recovering after several millennia of warming and retreat. Furthermore, the absence of advances beyond the present-day position during for example the 9.3 and 8.2 ka cold events as well as the early-Neoglacial suggest a substantial retreat during most of the Holocene.

Description: Publication date: 1 August 2018 Source: Quaternary Science Reviews, Volume 193 Author(s): Ping Liu, Feng Yue, Jiaqing Liu, Huafeng Qin, Shihu Li, Xiang Zhao, Jianwei Xu, Baoyin Yuan, Chenglong Deng, Rixiang Zhu The sedimentary sequence in Nihewan Basin, northern China, is rich in mammalian fossils and Paleolithic sites. Extensive magnetostratigraphic investigations have been carried out in the Nihewan sediments, but precise age control on the earliest Nihewan red sediments, which have a fluvio-lacustrine origin in the upper part and an eolian origin in the lower part, has remained unavailable. The formation process of Nihewan paleo-lake, therefore, remains unclear. Here we contribute to understanding the age of the early Nihewan reworked and eolian red clays by presenting detailed magnetostratigraphic and rock magnetic results from the Shixia section coupled with geochemical and petrographic analyses. Magnetostratigraphic correlation to the geomagnetic polarity timescale indicates that the Shixia sedimentary sequence recorded part of the Gilbert Chron with the onset of deposition of the Nihewan Formation occurring prior to the Gilbert-Gauss geomagnetic reversal at 3.6 Ma. With tectonic development of a graben basin, early red clay was deposited first in Nihewan Basin during the Early Pliocene before giving way to lacustrine environments in Nihewan paleo-lake. Geochemical and petrographic results indicate a wind-blown origin for the lower red clay deposits, which have been reworked and mixed with conglomerates produced by local tectonic activity to produce the basal Nihewan sediments. Later formation of carbonate nodules has given rise to the sediments that are now exposed in Nihewan Basin.

Description: Publication date: 1 August 2018 Source: Quaternary Science Reviews, Volume 193 Author(s): A. Schneider, G. Panieri, A. Lepland, C. Consolaro, A. Crémière, M. Forwick, J.E. Johnson, A. Plaza-Faverola, S. Sauer, J. Knies Multiple proxies in the geological record offshore NW Svalbard track shallow subseafloor diagenesis and seafloor methane seepage during the Last Glacial Maximum (LGM) extent and the disintegration of the Svalbard Barents Sea Ice Sheet (SBIS). Vestnesa Ridge, located at 79°N and in 1200 m water depth, is one of the northernmost known active methane seep sites and is characterised by a subseafloor fluid flow system, numerous seafloor pockmarks and gas flares in the water column. In this study, we develop a Late Pleistocene and Holocene stratigraphic framework, use stable oxygen and carbon isotope signatures (δ 18 O, δ 13 C) of benthic and planktic foraminifera, the mineralogical and carbon isotope composition of methane-derived authigenic carbonate (MDAC) and sediment geochemical data of ten sediment cores to assess methane seepage variability on Vestnesa Ridge. The studied cores cover the age range between 31.9 and 10 cal ka BP and record 32 negative δ 13 C excursions in benthic and planktic foraminifera with amplitudes down to −29 ‰ VPDB. These δ 13 C excursions are often associated with elevated Ca/Ti and Sr/Ti elemental ratios in sediments and MDAC nodules. The precipitation of MDAC overgrowth on foraminiferal tests explains most of the negative δ 13 C excursions. In this dataset, the oldest recorded methane emission episodes on Vestnesa Ridge occurred between the LGM (24–23.5 cal ka BP) and Heinrich Event 1 (HE 1; 17.7–16.8 cal ka BP). Geological indicators for past subseafloor methane cycling and seafloor methane seepage, such as negative foraminiferal δ 13 C excursions, MDAC nodules, and elevated Sr/Ti elemental ratios recorded in post-LGM sediments, possibly represent vertical migration of the sulphate-methane transition zone (SMTZ) and post-date sedimentation by up to 13.4 ka. However, it is important to note that indications of post-LGM seafloor methane seepage at Vestnesa Ridge also correspond to the established methane efflux chronology for the adjacent Barents Sea shelf, implying that glacio-isostatic adjustments and associated re-activation of pre-existing deep-seated faults after disintegration of the SBIS are likely important controlling factors on fluid migration towards the seafloor.

Description: Publication date: 1 August 2018 Source: Quaternary Science Reviews, Volume 193 Author(s): Hans Renssen, Hugues Goosse, Didier M. Roche, Heikki Seppä To analyze the global hydroclimate response during the Younger Dryas cold event, we evaluate climate model results that have been constrained with proxy-based temperatures from the North Atlantic region. We find that both the temperature and the hydroclimate response have a clear global signature. A marked cooling is simulated over the North Atlantic Ocean (more than 5 °C) and the downwind continents (2–4 °C). This response is related to the weakening of the Atlantic meridional overturning circulation under influence of meltwater discharges. The hydroclimate response is most expressed over Eurasia in a belt between 40 and 60°N, and over Northern Africa in the Sahel region. In both areas, a strong decrease in soil moisture is simulated (up to 20% reduction). In contrast, a striking increase in moisture is found over southeastern North America (15% increase), where southerly atmospheric flow brings moist air to the continent. Outside these areas that are clearly affected by the cold North Atlantic Ocean, the responses of temperature and moisture are decoupled, with different causes for these temperature and hydroclimate responses. In the tropics, the hydroclimate response is governed by the southward shift of the intertropical convergence zone (ITCZ) due to the cooling of the North Atlantic Ocean. This causes drier conditions north of the equator and wetter conditions in the Southern Hemisphere tropics. The associated changes in soil moisture are relatively gradual here, taking up to two centuries to complete, suggesting that the impact of the ITCZ shift on the tropical hydroclimate is building up. Our experiment indicates that Southern Hemisphere continents experienced a small cooling (less than 0.5 °C) during the Younger Dryas, caused by the negative radiative forcing associated with reduced atmospheric methane concentrations and enhanced dust levels. In our simulation, the bi-polar seesaw mechanism is relatively weak, so that the associated warming of the South Atlantic Ocean is not overwhelming the reduction in radiative forcing. Our results thus indicate that in the tropics and/or Southern Hemisphere, the cooling is a response to the negative radiative forcing, while the hydroclimatic changes are predominantly resulting from ITCZ variations. Consequently, when interpreting hydroclimatic proxy records from these regions, data should not be compared directly to key records from high latitudes, such as Greenland ice core stable isotope records.

Description: Publication date: 1 August 2018 Source: Quaternary Science Reviews, Volume 193 Author(s): F. Alayne Street-Perrott, Jonathan A. Holmes, Iain Robertson, Katherine J. Ficken, Tiiu Koff, Neil J. Loader, Jim D. Marshall, Tõnu Martma The well characterized oxygen-isotopic fractionation during cellulose biosynthesis has been utilised by numerous studies of stable isotopes in fine-grained aquatic cellulose. We measured the δ 13 C cellulose and δ 18 O cellulose values of bulk cellulose and moss fragments from an ∼11.4ka-long core obtained from a shallow, productive, spring-fed, hardwater lake, Äntu Sinijärv, Estonia (59˚3.8′N; 26˚14.5′E; 94.6 m a.s.l.; maximum depth 7.3 m), in order to reconstruct regional Holocene climate and lake-basin evolution. Isotopically, the modern waterbody is a well-behaved, open, hydrological system with negligible evaporative effects. Cellulose-isotope records were compared with down-core measurements of loss-on-ignition (LOI), carbonate and mineral contents, total organic carbon (TOC), total nitrogen (TN), C/N ratio, δ 13 C TOC , biomarker indices (P alg and P aq ), published palaeoecological data and a δ 18 O carbonate record from the same palaeolake. Green microalgae, freshwater macroalgae ( Chara ) and aquatic bryophytes were important sources of sedimentary cellulose during different phases in the environmental history of the lake. Although a strong palaeoclimatic imprint can be detected in the δ 18 O cellulose record from Äntu Sinijärv, notably the Preboreal oscillation, the 8.2ka event and an unnamed cold oscillation ∼3.25ka BP, the isotopic signal of these events may have been amplified by increases in 18 O-depleted spring snowmelt. In contrast, δ 13 C cellulose was tightly coupled to the Holocene evolution of terrestrial ecosystems and soils by significant inputs of biogenic carbon from the catchment and sublacustrine springs. During the early Holocene, ∼11 – 9ka BP, the δ 18 O cellulose and δ 18 O carbonate records diverge markedly, which can be attributed to “no-analogue” seasonal, climatic, hydrological and isotopic conditions resulting from orbital forcing and residual ice-sheet impacts.

Description: Publication date: 1 August 2018 Source: Quaternary Science Reviews, Volume 193 Author(s): Anning Cui, Chunmei Ma, Lin Zhao, Lingyu Tang, Yulian Jia High-resolution precipitation reconstructions of the Little Ice Age (LIA) are fundamental for investigating the driving mechanisms behind hydroclimatic changes, which would provide reference for predicting precipitation change in the future. However, current precipitation reconstructions mainly focus on mean conditions during the whole LIA, little attention was paid to internal changes. Here, we present a high-resolution precipitation reconstruction based on pollen records from the middle reaches of the Yangtze River, spanning from 1300 to 2010 CE. In this study, the LIA was defined as the period of 1300–1870 CE based on PC2 value and pollen assemblage, manifest as cold interval with internal fluctuations (early-LIA: 1300-1340 CE, mid-LIA: 1340-1720 CE and late-LIA: 1720-1870 CE). Negative PC1 value during the early-LIA and mid-LIA indicated dry condition, while positive PC1 value recorded wet late-LIA. Cold interval in the early-LIA increased effective moisture by reducing evaporation, which may contribute to high content pollen concentrations and wetland herbs pollen percentage. Dry condition in the mid-LIA probably induced by warm interval by increasing evaporation and less precipitation. During the late-LIA, high content pollen concentrations and more fine-grained sediment indicate there was standing water in the bog, which was induced by heavy precipitation and cold interval. Moisture variation recorded by PC1 value and grain size distribution indicated humidity-flip between the mid-LIA and late-LIA. This humidity-flip is also supported by the frequency of flood disasters reported in historical documents. Precipitation changes during the LIA could be associated with East Asian Summer Monsoon (EASM) and El Niño-Southern Oscillation (ENSO) variability. The dry early-LIA and mid-LIA caused by the weaker EASM and more La Niña-type conditions, during which the Western Pacific Subtropical High (WPSH) weakened and retreated northeastward, leading to less Mei-yu precipitation in the Yangtze River basin. Intensified EASM and more El Niño-type events during the late-LIA lead to longer Mei-yu season along the Yangtze River and more precipitation.

Description: Publication date: 1 August 2018 Source: Quaternary Science Reviews, Volume 193 Author(s): Duo Wu, Xuemei Chen, Feiya Lv, Mark Brenner, Jason Curtis, Aifeng Zhou, Jianhui Chen, Mark Abbott, Junqing Yu, Fahu Chen Proxy-based reconstructions of Holocene temperature show that both the timing and magnitude of the thermal maximum varied substantially across different regions. Given the ‘Holocene temperature conundrum’, it is becoming increasingly important to reconstruct seasonal temperature variations. As a major component of the global monsoon system, the Indian summer monsoon (ISM) transports moisture and heat from the tropical oceans to higher latitudes and thus it has substantial socioeconomic implications for its regions of influences. We developed a well-dated, pollen-based summer temperature record (mean July; MJT) for the last 14,000 years from Xingyun Lake in southwest China, where the climate is dominated by the ISM. MJT decreased during the Younger Dryas, increased slowly to high values during 8000–5500 yr BP, and decreased thereafter. The MJT record differs from that inferred using carbonate oxygen isotopes (δ 18 O) from the same sediment core. The latter record reflects variations in monsoon precipitation, with highest precipitation during the early Holocene (11,000–6500 yr BP). We propose that summer temperature and precipitation in southwest China were decoupled during the early Holocene. Both MJT and monsoon precipitation decreased after the middle Holocene, tracking the trend in boreal summer insolation. We suggest that greater cloud cover, associated with high precipitation and generated by a strong summer monsoon, may have depressed early Holocene temperatures that would otherwise be driven by greater summer insolation. Melting ice sheets in high-latitude regions and high concentrations of atmospheric aerosols during the early Holocene may also have contributed, in part, to the relatively cool summer temperatures.