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61.
Tong Lee Toshiyuki Awaji Magdalena Balmaseda Nicolas Ferry Yosuke Fujii Ichiro Fukumori Benjamin Giese Patrick Heimbach Armin Köhl Simona Masina Elisabeth Remy Anthony Rosati Michael Schodlok Detlef Stammer Anthony Weaver 《Dynamics of Atmospheres and Oceans》2010
Monthly averaged total volume transport of the Indonesian throughflow (ITF) estimated by 14 global ocean data assimilation (ODA) products that are decade to multi-decade long are compared among themselves and with observations from the INSTANT Program (2004–2006). The main goals of the comparisons are to examine the consistency and evaluate the skill of different ODA products in simulating ITF transport. The ensemble averaged, time-mean value of ODA estimates is 13.6 Sv (1 Sv = 106 m3/s) for the common 1993–2001 period and 13.9 Sv for the 2004–2006 INSTANT Program period. These values are close to the 15-Sv estimate derived from INSTANT observations. All but one ODA time-mean estimate fall within the range of uncertainty of the INSTANT estimate. In terms of temporal variability, the scatter among different ODA estimates averaged over time is 1.7 Sv, which is substantially smaller than the magnitude of the temporal variability simulated by the ODA systems. Therefore, the overall “signal-to-noise” ratio for the ensemble estimates is larger than one. The best consistency among the products occurs on seasonal-to-interannual time scales, with generally stronger (weaker) ITF during boreal summer (winter) and during La Nina (El Nino) events. The scatter among different products for seasonal-to-interannual time scales is approximately 1 Sv. Despite the good consistency, systematic difference is found between most ODA products and the INSTANT observations. All but the highest-resolution (18 km) ODA product show a dominant annual cycle while the INSTANT estimate and the 18-km product exhibit a strong semi-annual signal. The coarse resolution is an important factor that limits the level of agreement between ODA and INSTANT estimates. Decadal signals with periods of 10–15 years are seen. The most conspicuous and consistent decadal change is a relatively sharp increase in ITF transport during 1993–2000 associated with the strengthening tropical Pacific trade wind. Most products do not show a weakening ITF after the mid-1970s’ associated with the weakened Pacific trade wind. The scatter of ODA estimates is smaller after than before 1980, reflecting the impact of the enhanced observations after the 1980s. To assess the representativeness of using the average over a three-year period (e.g., the span of the INSTANT Program) to describe longer-term mean, we investigate the temporal variations of the three-year low-pass ODA estimates. The average variation is about 3.6 Sv, which is largely due to the increase of ITF transport from 1993 to 2000. However, the three-year average during the 2004–2006 INSTANT Program period is within 0.5 Sv of the long-term mean for the past few decades. 相似文献
62.
The solid planets assembled 4.57 Gyr ago during a period of less than 100 Myr, but the bulk of the impact craters we see on the inner planets formed much later, in a narrow time interval between 3.8 and 3.9 Gyr ago, during the so-called late heavy bombardment (LHB). It is not certain what caused the LHB, and it has not been well known whether the impactors were comets or asteroids, but our present study lend support to the idea that it was comets. Due to the Earth’s higher gravity, the impactors will have hit the Earth with ∼twice the energy density that they hit the Moon, and the bombardment will have continued on Earth longer than on the Moon. All solid surface of the Earth will have been completely covered with craters by the end of the LHB.However, almost nothing of the Earth’s crust from even the end of this epoch, is preserved today. One of the very few remnants, though, is exposed as the Isua greenstone belt (IGB) and nearby areas in Western Greenland. During a field expedition to Isua, we sampled three types of metasedimentary rocks, deposited ∼3.8 billion years ago, that contain information about the sedimentary river load from larger areas of surrounding land surfaces (mica-schist and turbidites) and of the contemporaneous seawater (BIF). Our samples show evidence of the LHB impacts that took place on Earth, by an average of a seven times enrichment (150 ppt) in iridium compared to present-day ocean crust (20 ppt). The clastic sediments show slightly higher enrichment than the chemical sediments, which may be due to contamination from admixtures of mafic (proto-crustal) sources.We show that this enrichment is in agreement with the lunar cratering rate and a corresponding extraterrestrial LHB contribution to the Earth’s Hadean-Eoarchean crust, provided the bulk of the influx was cometary (i.e., of high velocity and low in CI abundance), but not if the impactors were meteorites (i.e. had velocities and abundances similar to present-day Earth-crossing asteroids). Our study is a first direct indication of the nature of the LHB impactors, and the first to find an agreement between the LHB lunar cratering rate and the Earth’s early geochemical record (and the corresponding lunar record). The LHB comets that delivered the iridium we see at Isua will at the same time have delivered the equivalent of a ∼1 km deep ocean, and we explain why one should expect a cometary ocean to become roughly the size of the Earth’s present-day ocean, not only in terms of depth but also in terms of the surface area it covers. The total impacting mass on the Earth during the LHB will have been ∼1000 tons/m2. 相似文献
63.
Nikki Dijkstra Nadine B. Quintana Krupinski Masako Yamane Stephen P. Obrochta Yosuke Miyairi Yusuke Yokoyama Caroline P. Slomp 《Estuaries and Coasts》2018,41(1):139-157
Salinity variations in restricted basins like the Baltic Sea can alter their vulnerability to hypoxia (i.e., bottom water oxygen concentrations <2 mg/l) and can affect the burial of phosphorus (P), a key nutrient for marine organisms. We combine porewater and solid-phase geochemistry, micro-analysis of sieved sediments (including XRD and synchrotron-based XAS), and foraminiferal δ18O and δ13C analyses to reconstruct the bottom water salinity, redox conditions, and P burial in the Ångermanälven estuary, Bothnian Sea. Our sediment records were retrieved during the Integrated Ocean Drilling Program (IODP) Baltic Sea Paleoenvironment Expedition 347 in 2013. We demonstrate that bottom waters in the Ångermanälven estuary became anoxic upon the intrusion of seawater in the early Holocene, like in the central Bothnian Sea. The subsequent refreshening and reoxygenation, which was caused by gradual isostatic uplift, promoted P burial in the sediment in the form of Mn-rich vivianite. Vivianite authigenesis in the surface sediments of the more isolated part of the estuary ultimately ceased, likely due to continued refreshening and an associated decline in productivity and P supply to the sediment. The observed shifts in environmental conditions also created conditions for post-depositional formation of authigenic vivianite, and possibly apatite formation, at ~8 m composite depth. These salinity-related changes in redox conditions and P burial are highly relevant in light of current climate change. The results specifically highlight that increased freshwater input linked to global warming may enhance coastal P retention, thereby contributing to oligotrophication in both coastal and adjacent open waters. 相似文献
64.
Characteristics of coastal-trapped waves induced by typhoon along the southeast coast of Honshu,Japan 总被引:1,自引:0,他引:1
Mooring observations using ADCP, electromagnetic current meters and thermometers were performed to clarify the vertical and
horizontal structure of coastal-trapped waves (CTWs) on continental shelf and slope on the eastern side of Sagami Bay, Japan,
in August and September 2003. A strong inflow associated with CTW caused by Typhoon 0315 (CTW15) was observed with remarkable
downwelling. The maximum current due to CTW15 was over 100 cm s−1, confined to the upper layer shallower than 90 m. The CTW (CTW10) induced by Typhoon 0310, was associated with the coastal
upwelling and maximum outflow was 33 cm s−1; the currents were extended near the bottom at 230 m depth. Remarkable discrepancies were found between the current structures
of CTWs. CTW15 was explained by superposing the second CTW mode on the first CTW mode, whereas CTW10 was explained by the
first CTW mode. The generation and propagation processes of both CTWs were reproduced by numerical experiments using a three-dimensional
level model. The model results indicated that the difference of modal characteristics between CTW15 and CTW10 already exists
in the CTW generation region and are due to difference of the wind direction, i.e., the typhoon’s path. 相似文献
65.
A numerical experiment using a three dimensional level model was performed to clarify the mechanism generating a strong coastal
current, Kyucho, induced by the passage of Typhoon 0406 around the tip of the Tango Peninsula, Japan in June 2004. Wind stress accompanied
by Typhoon 0406 was applied to the model ocean with realistic bottom topography and stratification condition. The model well
reproduced the characteristics of Kyucho observed by Kumaki et al. (2005), i.e., the strong alongshore current with maximum velocity of 53 cm s−1 and its propagation along the peninsula with propagation speed of about 0.6 m s−1 one half-day after the typhoon’s passage. Coastal-trapped waves (CTW) accompanied by downwelling were induced along the northwest
coast of the peninsula by the alongshore wind stress. The energy density flux due to the CTW flowed eastward along the coast,
and indicated scattering of the CTW around the eastern coast of the peninsula. In addition, significant near-inertial internal
gravity waves were also caused in the offshore region from the west of the Noto Peninsula to the north of the Tango Peninsula
by the typhoon’s passage. The energy flux density of the near-inertial fluctuations flowed southward off the Fukui coast,
and part of the energy flux was trapped on the tip of the Tango Peninsula, flowing with the coast on its right. It was found
that the strong current, Kyucho, at the northeastern tip of the Tango Peninsula was generated by superposition of the near-inertial internal gravity waves
and subinertial CTW. 相似文献
66.
Twenty-six of the fifty-seven stone meteorites listed in Huss (1979) from Roosevelt County, New Mexico, have been classified in the present study. Microprobe analyses indicate 15 H type, 9 L type and 2 LL type chondrites. Based on compositional, textural, and locational comparisons, as many as 10 chondrites may be paired to three distinct falls. 相似文献
67.
Multiple-rind structure is common among shallow-water pillows with diameters larger than about 1 m in Oamaru, New Zealand, on the Columbia Plateau (USA), and elsewhere. A rind consists of sideromelane, tachylyte, and tachylytic basalt. A multiple rind is a concentric set of repeated rinds in various forms, e. g., a portion of a broken rind thrust under another part, a series of short and detached subparallel rinds, or a pouch-shaped depression. Transitions and combinations of these three forms are common. Multiple-rind structure develops at any part of the pillow perimeter, but does not cover the pillow completely. It is always accompanied by a rupture in the outermost rind. Up to 13 rinds have been observed, but two to four rinds are most common. The multiple-rind structure is formed by implosion resulting from condensation of exsolved H2O. When H2O condenses, a pressure difference between the interior and exterior of a pillow is created. Above a certain threshold pressure difference, the outer skin of a pillow is torn at weak points, such as radial joints, and thrusts under the neighboring skin, buckles to form a pouch-shaped depression, or produces some variation of these. One set of multiple rinds is thus formed. Further exsolution and condensation of H2O in solidifying pillows may cause development of additional rinds. H2O exsolution and condensation and subsequent implosion are limited to low-pressure environments so that multiple-rind structure is characteristic of shallow-water pillow lava. 相似文献
68.
About 2000 active faults are known to exist within the land area of Japan. Most of these active faults have deformed the topographic surfaces which were formed in the late Quaternary, including fluvial terraces; and the formative ages of these terraces are estimated mainly by tephrochronology. Fluvial terraces in the eastern Hokuriku region, comprising the Toyama, Tonami, and Kanazawa Plains, northern central Japan, are widely distributed and have been deformed by reverse active faults. The formative age of terraces in this area has not been reported, as volcanic ash deposits are rarely visible within terrace deposits and the overlying loamy soil, and outcrops of fluvial terraces are quite scarce in this area. In the present study, we carried out a drilling survey on these terraces to obtain samples of the overlying loamy soil and upper part of terrace deposits. From these samples, we extracted some well-known widespread volcanic ash, from which we were able to estimate the approximate age of the terraces and the vertical slip rate of the active faults. Late Quaternary fluvial terraces in eastern Hokuriku are divided into 12 levels: Terraces 1 to 12 in descending order. Widespread tephras such as the Kikai-Tozurahara Tephra (K-Tz: 95 ka) are contained in the lowest part of the loamy soil in Terrace 4 and the Daisen-Kurayoshi Pumice (DKP: 55 ka) is present in the lowest part of the loamy soil in Terrace 6. From the ages and the vertical displacements of the fluvial terraces, the late Quaternary average vertical slip rates of active faults in eastern Hokuriku are estimated to be 0.2–0.9 mm/year (Uozu fault), 0.1–0.4 mm/year (Kurehayama fault), 0.1–0.3 mm/year (Takashozu fault), 0.1–0.4 mm/year (Hohrinji fault), and 0.5–0.8 mm/year (Morimoto-Togashi fault). We also estimated the recurrence interval of earthquakes related to active faults from displacement per event and ages of terraces and no significant difference in vertical displacement per single earthquake for different active faults, and recurrence intervals tend to be inversely proportional to vertical displacement rates. This study demonstrates that a combination of drilling of loamy soil and precise cryptotephra analysis of fluvial terraces can be used to estimate the formative age of the terraces and the average slip rate of active faults in areas where volcanic ash deposits are rare. 相似文献
69.
Assessment of future precipitation indices in the Shikoku region using a statistical downscaling model 总被引:1,自引:1,他引:0
Kenichi Tatsumi Tsutao Oizumi Yosuke Yamashiki 《Stochastic Environmental Research and Risk Assessment (SERRA)》2014,28(6):1447-1464
In this study, we used the statistical downscaling model (SDSM) to estimate mean and extreme precipitation indices under present and future climate conditions for Shikoku, Japan. Specifically, we considered the following mean and extreme precipitation indices: mean daily precipitation, R10 (number of days with precipitation >10 mm/day), R5d (annual maximum precipitation accumulated over 5 days), maximum dry-spell length (MaDSL), and maximum wet-spell length (MaWSL). Initially, we calibrated the SDSM model using the National Center for environmental prediction (NCEP) reanalysis dataset and daily time series of precipitation for ten locations in Shikoku which were acquired from the surface weather observation point dataset. Subsequently, we used the validated SDSM, using data from NCEP and outputs form general circulation models (GCM), to predict future precipitation indices. Specifically, the HadCM3 GCM was run under the special report on emissions scenarios (SRES) A2 and B2 scenarios, and the CGCM3 GCM was run under the SRES A2 and A1B scenarios. The results showed that: (1) the SDSM can reasonably be used to simulate mean and extreme precipitation indices in the Shikoku region; (2) the values of annual R10 were predicated to decrease in the future in northern Shikoku under all climate scenarios; conversely, the values of annual R10 were predicted to increase in the future in the range of 0–15 % in southern and western Shikoku. The values of annual MaDSL were predicted to increase in northern Shikoku, and the values of annual MaWSL were predicted to decrease in northeastern Shikoku; (3) the spatial variation of precipitation indices indicated the potential for an increased occurrence of drought across northeastern Shikoku and an increased occurrence of flood events in the southwestern part of Shikoku, especially under the A2 and A1B scenarios; (4) characteristics of future precipitation may differ between the northern and southern sides of the Shikoku Mountains. Regional variations in extreme precipitation indices were not notably evident in the B2 scenario compared to the other scenarios. 相似文献
70.
Evidence for abrupt coastal uplifts has been found in emerged sessile assemblages in a sea cave at the southern end of the Izu Peninsula, central Japan. We identified five sessile assemblage zones: Zones I to V, in ascending order. The uppermost zone (Zone I), located at an elevation of 2.7–3.5 m above the present‐day mean sea level (amsl), is a hard massive shellcrust consisting mainly of the barnacles Chthamalus challenger and the tube worm Pomatoleios kraussii. Zone II, at 2.35–2.7 m amsl, is dominated by well‐preserved individuals of C. challenger. Zone III, at 2.0–2.35 m amsl, is strongly eroded and consists mainly of C. challenger and P. kraussii. Zone IV, at 1.6–2.0 m amsl, is characterized by the co‐occurrence of very fresh shells of C. challenger and P. kraussii. Zone V (the lowest zone), at 1.0–1.60 m amsl, is characterized by the co‐occurrence of very fresh shells of Saccostrea kegaki and P. kraussii, and by the absence of C. challenger. Radiocarbon dating by accelerator mass spectrometry (AMS) and the presence of modern taxa in the sessile assemblages suggest that three episodes of coastal uplift have occurred in the area, during AD 570–820, AD 1000–1270, and AD 1430–1660, with magnitudes of 0.9–2.0 m, 0.3–0.8 m, and 1.9–2.2 m, respectively. 相似文献