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Many studies are reconstructing flood records in the continental margins during the middle to late-Holocene. However, distinguishing the frequency and magnitude of flood events was difficult. Light gray event layers (GELs) in the sediment of Lake Suigetsu in Central Japan can solve this problem because they are recording the occurrence and magnitude of flood events during the last 80 years. Using these GELs, we aimed to reconstruct the frequency and magnitude of flood events during the last 8000 years. First, we verified whether GELs maintained the recording of flood events. We found that thin GELs (less than 40 mg/cm2 in mass) were rare, probably because of bioturbation, whereas thick GELs (larger than 40 mg/cm2 in mass) were rarely erased. We also found that GELs formed by the same amount of rainfall could have been thinner before 100 years ago. We revealed that the occurrence of extreme flood-origin event layers (EFELs: GELs thicker than 40 mg/cm2) during the last 8000 years may indicate the occurrence of extreme flood events (EFEs). Mass accumulation of EFELs may indicate the minimum estimation of rainfall on EFEs. There are several periods with higher frequency and magnitude of EFEs than those of the present level, agreeing with the periods of high flood activity in western Japan and East China. The frequency and magnitude of EFEs show different temporal variations. Northward and southward shifts in the westerly jet and monsoon fronts can partially explain such patterns. [ABSTRACT FROM AUTHOR]

Changes in the geometry of ocean Meridional Overturning Circulation (MOC) are crucial in controlling changes of climate and the carbon inventory of the atmosphere. However, the precise timing and global correlation of short-term glacial-to-deglacial changes of MOC in different ocean basins still present a major challenge. A possible solution is offered by the fine structure of jumps and plateaus in the record of radio-carbon (14C) concentration of the atmosphere and surface ocean that reflects changes in atmospheric 14C production as well as in the 14C exchange between air and sea and within the ocean. Boundaries of atmospheric 14C plateaus in the 14C record of Lake Suigetsu, now tied to Hulu U/Th model-ages instead of optical varve counts, provide a stratigraphic "rung ladder" of ~30 age tie points from 29 to 10 ka for correlation with and dating of planktic oceanic 14C records. The age difference between contemporary planktic and atmospheric 14C plateaus gives an estimate of the global distribution of 14C reservoir ages for surface waters of the Last Glacial Maximum (LGM) and deglacial Heinrich Stadial 1 (HS-1), as shown by 19 planktic 14C records. Clearly elevated and variable reservoir ages mark both high-latitude sites covered by sea ice and/or meltwater and upwelling regions. 14C ventilation ages of LGM deep waters reveal opposed geometries of Atlantic and Pacific MOC. Similar to today, Atlantic deep-water formation went along with an estuarine inflow of old abyssal waters from the Southern Ocean up to the northern North Pacific and an outflow of upper deep waters. Vice versa, 14C ventilation ages suggest a reversed MOC during early HS-1 and a ~1500 year long flushing of the deep North Pacific up to the South China Sea, when estuarine circulation geometry marked the North Atlantic, gradually starting near 19 ka. Elevated 14C ventilation ages of LGM deep waters reflect a major drawdown of carbon from the atmosphere. Inversely, the subsequent massive age drop and change in MOC induced two major events of carbon release to the atmosphere as recorded in Antarctic ice cores, shifts that highlight the significance of ocean MOC for atmospheric CO2 and its 14C inventory. These new features of MOC and the carbon cycle offer a challenge to model simulations that, in part because of insufficient spatial model resolution and reference data for testing the model results, still poorly reproduce them. [ABSTRACT FROM AUTHOR]

The luminescence characteristics of sediments are affected by a variety of environmental factors, reflecting both local and broader regional influences. If seeking to apply optically-stimulated luminescence (OSL) as a 'pure' dating technique, variability in these external variables needs to be controlled for, involving, inter alia, lengthy pretreatment procedures and complex dose rate corrections. However, in so doing, a lot of potentially valuable palaeoenvironmental information is lost. Instead, in the present study, we explicitly analysed raw, non-pretreated sediment that preserves this wealth of contributory environmental influence. Using a SUERC portable optically-stimulated luminescence (POSL) reader [1], we have performed rapid profiling across a 20,000 year interval of the annually laminated (varved) Lake Suigetsu sedimentary profile, central Japan (i.e., 30,000 to 50,000 cal BP) [2], producing 443 contiguous measurements with a mean sampling resolution of 45 years. To facilitate our understanding of this dataset, follow-up, more targeted laboratory profiling techniques were applied. The 'cryptostratigraphy' ('hidden stratigraphy') revealed by our data includes the identification of a step-change in luminescence parameters circa 39,200 cal BP, which we attribute to a major earthquake that resulted in re-routing of inflow to the lake. Further variability in the derived luminescence signals are compared with supporting palynological, palaeomagnetic [3], µXRF [4], and thin-section microscopy data [5] from Lake Suigetsu. A potential correlation between the luminescence profile and geomagnetic field intensity is tantalising [6], and will be the focus of discussion.e [ABSTRACT FROM AUTHOR]

The varved sediment of Lake Suigetsu (central Japan) provides a valuable opportunity to obtain high-resolution, multi-proxy palaeoenvironmental data across the last glacial/interglacial cycle. In order to maximize the potential of this archive, a well-constrained chronology is required. This paper outlines the multiple geochronological techniques being applied - namely varve counting, radiocarbon dating, tephrochronology (including argon-argon dating) and optically stimulated luminescence ( OSL) - and the approaches by which these techniques are being integrated to form a single, coherent, robust chronology. Importantly, we also describe here the linkage of the floating Lake Suigetsu ( SG06) varve chronology and the absolute ( Int Cal09 tree-ring) time scale, as derived using radiocarbon data from the uppermost (non-varved) portion of the core. This tie-point, defined as a distinct (flood) marker horizon in SG06 (event layer B-07-08 at 1397.4 cm composite depth), is thus derived to be 11 255 to 11 222 Int Cal09 cal. years BP (68.2% probability range). [ABSTRACT FROM AUTHOR]

Calibration is a fundamental stage of the radiocarbon (14C) dating process if one is to derive meaningful calendar ages from samples' 14C measurements. For the first time, the IntCal09 calibration curve (Reimer et al. 2009) provided an internationally ratified calibration data set across almost the complete range (0 to 50,000 cal BP) of the 14C timescale. However, only the last 12,550 cal yr of this record are composed of terrestrial data, leaving approximately three quarters of the 14C timescale necessarily calibrated via less secure, marine records (incorporating assumptions pertaining to the temporally variable "marine reservoir effect"). The predominantly annually laminated (varved) sediment profile of Lake Suigetsu, central Japan, offers an ideal opportunity to derive an extended terrestrial record of atmospheric 14C across the entire range of the method, through pairing of 14C measurements of terrestrial plant macrofossil samples (extracted from the sediment) with the independent chronology provided through counting of its annual laminations. This paper presents new data (182 14C determinations) from the upper (largely non-varved) 15 m of the Lake Suigetsu (SG06) sediment strata. These measurements provide evidence of excellent coherence between the Suigetsu 14C data and the IntCal09 calibration curve across the last ~12,000 cal yr (i.e. the portion of IntCal based entirely on terrestrial data). Such agreement demonstrates that terrestrial plant material picked from the Lake Suigetsu sediment provides a reliable archive of atmospheric 14C, and therefore supports the site as being capable of providing a high-resolution extension to the "wholly terrestrial" (i.e. non-reservoir-corrected) calibration curve beyond its present 12,550 cal BP limit. [ABSTRACT FROM AUTHOR]