Lithospheric organic carbon ("petrogenic"; OC
) is oxidized during exhumation and subsequent erosion of mountain ranges. This process is a considerable source of carbon dioxide (CO
) to the ...atmosphere over geologic time scales, but the mechanisms that govern oxidation rates in mountain landscapes are poorly constrained. We demonstrate that, on average, 67 ± 11% of the OC
initially present in bedrock exhumed from the tropical, rapidly eroding Central Range of Taiwan is oxidized in soils, leading to CO
emissions of 6.1 to 18.6 metric tons of carbon per square kilometer per year. The molecular and isotopic evolution of bulk OC and lipid biomarkers during soil formation reveals that OC
remineralization is microbially mediated. Rapid oxidation in mountain soils drives CO
emission fluxes that increase with erosion rate, thereby counteracting CO
drawdown by silicate weathering and biospheric OC burial.
Early researchers of radiocarbon levels in Southern Hemisphere tree rings identified a variable North-South hemispheric offset, necessitating construction of a separate radiocarbon calibration curve ...for the South. We present here SHCal20, a revised calibration curve from 0–55,000 cal BP, based upon SHCal13 and fortified by the addition of 14 new tree-ring data sets in the 2140–0, 3520–3453, 3608–3590 and 13,140–11,375 cal BP time intervals. We detail the statistical approaches used for curve construction and present recommendations for the use of the Northern Hemisphere curve (IntCal20), the Southern Hemisphere curve (SHCal20) and suggest where application of an equal mixture of the curves might be more appropriate. Using our Bayesian spline with errors-in-variables methodology, and based upon a comparison of Southern Hemisphere tree-ring data compared with contemporaneous Northern Hemisphere data, we estimate the mean Southern Hemisphere offset to be 36 ± 27 14C yrs older.
Calendar-dated tree-ring sequences offer an unparalleled resource for high-resolution paleoenvironmental reconstruction. Where such records exist for a few limited geographic regions over the last ...8,000 to 12,000 years, they have proved invaluable for creating precise and accurate timelines for past human and environmental interactions. To expand such records across new geographic territory or extend data for certain regions further backward in time, new applications must be developed to secure “floating” (not yet absolutely dated) tree-ring sequences, which cannot be assigned single-calendar year dates by standard dendrochronological techniques. This study develops two approaches to this problem for a critical floating tree-ring chronology from the East Mediterranean Bronze–Iron Age. The chronology is more closely fixed in time using annually resolved patterns of 14C, modulated by cosmic radiation, between 1700 and 1480 BC. This placement is then tested using an anticorrelation between calendardated tree-ring growth responses to climatically effective volcanism in North American bristlecone pine and the Mediterranean trees. Examination of the newly dated Mediterranean tree-ring sequence between 1630 and 1500 BC using X-ray fluorescence revealed an unusual calcium anomaly around 1560 BC. While requiring further replication and analysis, this anomaly merits exploration as a potential marker for the eruption of Thera.
During solar storms, the Sun expels large amounts of energetic particles (SEP) that can react with the Earth's atmospheric constituents and produce cosmogenic radionuclides such as
C,
Be and
Cl. Here ...we present
Be and
Cl data measured in ice cores from Greenland and Antarctica. The data consistently show one of the largest
Be and
Cl production peaks detected so far, most likely produced by an extreme SEP event that hit Earth 9125 years BP (before present, i.e., before 1950 CE), i.e., 7176 BCE. Using the
Cl/
Be ratio, we demonstrate that this event was characterized by a very hard energy spectrum and was possibly up to two orders of magnitude larger than any SEP event during the instrumental period. Furthermore, we provide
Be-based evidence that, contrary to expectations, the SEP event occurred near a solar minimum.
Baffin Bay hosts the largest and most productive of the Arctic polynyas: the North Water (NOW). Despite its significance and active role in water mass formation, the history of the NOW beyond the ...observational era remains poorly known. We reconcile the previously unassessed relationship between long-term NOW dynamics and ocean conditions by applying a multiproxy approach to two marine sediment cores from the region that, together, span the Holocene. Declining influence of Atlantic Water in the NOW is coeval with regional records that indicate the inception of a strong and recurrent polynya from ~ 4400 yrs BP, in line with Neoglacial cooling. During warmer Holocene intervals such as the Roman Warm Period, a weaker NOW is evident, and its reduced capacity to influence bottom ocean conditions facilitated northward penetration of Atlantic Water. Future warming in the Arctic may have negative consequences for this vital biological oasis, with the potential knock-on effect of warm water penetration further north and intensified melt of the marine-terminating glaciers that flank the coast of northwest Greenland.
Radiocarbon dating is the most widely applied dating method in archaeology, especially in human evolution studies, where it is used to determine the chronology of key events, such as the replacement ...of Neanderthals by modern humans in Europe. However, the method does not always provide precise and accurate enough ages to understand the important processes of human evolution. Here we review the newest method developments in radiocarbon dating ('Radiocarbon 3.0'), which can lead us to much better chronologies and understanding of the major events in recent human evolution. As an example, we apply these new methods to discuss the dating of the important Palaeolithic site of Bacho Kiro (Bulgaria).
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
There is a converging body of evidence supporting a measurable slowdown of the Atlantic Meridional Overturning Circulation (AMOC) as climate warms and Northern Hemisphere ice sheets inexorably ...shrink. Within this context, we assess the variability of the AMOC during the Holocene based on a marine sediment core retrieved from the deep northwest Atlantic, which sensitively recorded large‐scale deglacial transitions in deep water circulation. While there is a diffuse notion of Holocene variability in Labrador and Nordic Seas overturning, we report a largely invariable deep water circulation for the last ~11,000 years, even during the meltwater pulse associated with the 8.2‐ka event. Sensitivity tests along with high‐resolution 231Pa/230Th data constrain the duration and the magnitude of possible Holocene AMOC variations. The generally constant baseline during the Holocene suggests attenuated natural variability of the large‐scale AMOC on submillennial timescales and calls for compensating effects involving the upstream components of North Atlantic Deep Water.
Key Points
High‐resolution 231Pa/230Th record from the Bermuda Rise for the past 11,000 years presented
Low variability of Holocene AMOC derived from 231Pa/230Th, εNd and δ13C
Duration and magnitude of the 8.2‐ka event constrained by sensitivity tests
Abstract Abrupt radiocarbon ( 14 C) excursions, or Miyake events, in sequences of radiocarbon measurements from calendar-dated tree-rings provide opportunities to assign absolute calendar dates to ...undated wood samples from contexts across history and prehistory. Here, we report a tree-ring and 14 C-dating study of the Neolithic site of Dispilio, Northern Greece, a waterlogged archaeological site on Lake Kastoria. Findings secure an absolute, calendar-dated time using the 5259 BC Miyake event, with the final ring of the 303-year-long juniper tree-ring chronology dating to 5140 BC. While other sites have been absolutely dated to a calendar year through 14 C-signature Miyake events, Dispilio is the first European Neolithic site of these and it provides a fixed, calendar-year anchor point for regional chronologies of the Neolithic.
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