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Radiocarbon dating is the most widely applied and reliable dating technique for providing chronological control during Marine Isotope Stage 3 (MIS3; ∼60–27 cal kyr BP). Past variations in the atmospheric concentration of radiocarbon mean a calibration curve is required. IntCal20 and SHCal20 calibration curves covering MIS3 are presently largely based on non-atmospheric records which, in combination with larger radiocarbon (14C) dating uncertainties, results in significant smoothing and reduced resolution in calibration curve structure. Floating tree ring radiocarbon chronologies that are wiggle-matched to other palaeo records (particularly to Hulu Cave speleothems) have the potential to provide detailed structure to the MIS3 portion of extant calibration curves. New Zealand subfossil kauri (Agathis australis) trees are long-lived and are useful for constructing temporally-floating MIS3 atmospheric radiocarbon datasets. This paper presents extant and emerging data from several important Northland subfossil kauri locations (Omaha, Babylon Coast, Bream Bay, Kai Iwi Lakes, Mangawhai). We show the span of seven floating MIS3 kauri sequences (individual trees and chronologies) from which sequential radiocarbon series covering a total of 7556 years is now in development (representing 23% of the period 60–27 cal kyr BP). We also report radiocarbon dates for an additional 34 ancient kauri from MIS3 that can provide additional coverage. After these floating subfossil wood sequences have been produced, close to 40% of MIS3 (12,420 years) will be covered by contiguous subfossil kauri radiocarbon measurements. Based on our findings, we discuss the prospects and limitations for obtaining a highly resolved and precise atmospheric radiocarbon calibration curve comprehensively covering MIS3 using subfossil kauri. [ABSTRACT FROM AUTHOR]

This work presents a new, very long snowfall time series collected in a remote site of Italian Apennine mountains (Montevergine Observatory, 1280 m above sea level). After a careful check, based on quality control tests and homogenization procedures, the available data (i.e. daily height of new snow) have been aggregated over winter season (December–February) to study the long-term variability for the period 1884–2020. The main evidence emerging from this analysis lies in (i) the strong interannual variability of winter snowfall amounts, (ii) the absence of a relevant trend from the late 19th century to the mid-1970s, (iii) the strong reduction in the snowfall amount and frequency of occurrence from the mid-1970s to the end of the 1990s and (iv) the increase in average snowfall amount and frequency of occurrence in the past 20 years. Moreover, this study shed light on the relationship between the snowfall variability observed in Montevergine and the large-scale atmospheric circulation. Six different synoptic types, describing the meteorological scenarios triggering the snow events in the study area, have been identified by means of a cluster analysis, using two essential atmospheric variables, the 500 hPa geopotential height and the sea level pressure (both retrieved from the third version of the Twentieth Century Reanalysis dataset, which is available for the 1884–2015 period). Such patterns trace out scenarios characterized by the presence of a blocking high-pressure anomaly over Scandinavia or the North Atlantic and by a cold air outbreak involving both maritime and continental cold air masses. A further analysis demonstrates that the identified synoptic types are strongly related with different teleconnection patterns, i.e. the Arctic Oscillation (AO), the Eastern Atlantic Western Russia (EAWR), the Eastern Mediterranean Pattern (EMP), the North Atlantic Oscillation (NAO) and the Scandinavian pattern (SCAND), that govern the European winter atmospheric variability. The relevant decline in snowfall frequency and amounts between the 1970s and 1990s can be mainly ascribed to the strong positive trend of AO and NAO indices, which determined, in turn, a decrease in the incidence of patterns associated with the advection, in central Mediterranean area, of moist and cold arctic maritime air masses. The recent increase in average snowfall amounts can be explained by the reverse trend of the AO index and by the prevalence of a neutral or negative EAWR pattern. [ABSTRACT FROM AUTHOR]

Meteorological drought, or a prolonged period of below average precipitation, is a significant and recurring hazard in Northland, where eight droughts, all having severe negative impacts, have been recorded since 1900. The cause of drought is usually the persistence of slow-moving or blocking high-pressure systems over Northland during the summer seasons. The reasons for this behaviour and the links between severe drought occurrence and natural climate fluctuations caused by the El Niño-Southern Oscillation, the Interdecadal Pacific Oscillation and the Southern Annular Mode are poorly understood. An analysis of meteorological droughts, characterised by severity, duration, and frequency (return period) is undertaken for the period 1893-2018. Severity is measured by the Standardized Precipitation Index (SPI) and severity-duration-frequency relationships are described for 298 Northland rain gauge sites using copulas. The worst year in terms of monthly SPI values was 1993 when nearly 25% of all sites were affected by drought. Based on severity alone the worst drought (severity = 21.19 at Whangärei Harbour) occurred in 1987 and had a duration of 10 months and the three worst drought years were (in order) 1987, 1913 and 1990. Based on duration alone the worst drought occurred in 1993 at Topuni with a duration of 16 months and the three worst drought years were (in order) 1993, 1913 and 1986. Statistical tests of SPI values showed no consistent and significant temporal trend in drought occurrence in the 125-year period. Attempts at contouring and clustering demonstrated that SPI relationships are not spatially dependent, implying that there are no specific drought-prone areas and that drought may occur at any locality and time in Northland (given the appropriate synoptic conditions). Further work is needed to improve climatological understanding of drought occurrence, along with continued monitoring of drought conditions. Use of multivariate copulas, including extra variables such as minimum SPI values and spatial extent, should provide a more comprehensive description of drought in Northland. [ABSTRACT FROM AUTHOR]