Reconstructing pre-colonial oyster demographics in the Chesapeake Bay, USA

Recent estimates of growth and mortality rates in extant Chesapeake Bay, USA oyster (Crassostrea virginica) populations are used to quantify changes in both population abundance (dN/dT) and shell accretion (dS/dT) associated with modern population demographics. The demographics of oyster populations that would be required to maintain reef accretion rates commensurate with sea level rise over geological time frames are examined using estimates of oyster longevity in pre-colonial (pre -1600) times combined with parallel estimates of pre-disease endemic mortality. The analysis demonstrates that modern populations, with their disease related, age-truncated demographics, are generally not capable of maintaining and building biogenic reefs through accretion. Estimates of filtration rates associated with Chesapeake Bay oyster populations prior to 1600 considerably underestimate actual benthic-pelagic coupling during that period. Pristine oyster populations would have supported water column turnover rates on the order of minutes to hours. Thus, the spatial footprint of oyster reefs was limited by available productivity in the estuary. Accretion rate calculations for pristine (pre-1600) oyster reefs describe the intimate relationship between benthic-pelagic coupling and the presence or absence of oyster reefs and the associated communities.     

Miocene-to-recent structure and basinal architecture along the Central Range strike-slip fault zone, eastern offshore Trinidad

Previous GPS-based geodetic studies and onland paleoseismologic studies in Trinidad have shown that the 50-km-long, linear, onland segment of the Central Range fault zone (CRFZ) accommodates at least 60% of the total rate of right-lateral displacement (∼20 mm/yr) between the Caribbean and South American plates. 2D and 3D seismic reflection data from a 60-km-long and 30-km-wide swath of the eastern shelf of Trinidad (block 2AB) were used to map the eastern offshore extension of this potentially seismogenic and hazardous fault system and to document its deeper structure and tectonic controls on middle Miocene to recent clastic stratigraphy. Two unconformity surfaces and seafloor were mapped using 3D seismic data to generate isochron maps and to illustrate the close control of the CRFZ and associated secondary faults on small, clastic basins formed along its anastomosing strands and the east-west-striking North Darien Ridge fault zone (NDRFZ) that exhibits a down-to-the-north normal throw. Mapped surfaces include: 1) the middle Miocene angular unconformity, a prominent, regional unconformity surface separating underlying thrust-deformed rocks from a much less deformed overlying section; this regional unconformity is well studied from onland outcrops in Trinidad and in other offshore areas around Trinidad; 2) a Late Neogene angular unconformity developed locally within block 2AB that is not recognized in Trinidad; and 3) the seafloor of the eastern Trinidad shelf which exhibits linear scarps for both the CRFZ and the east-west-striking North Darien Ridge fault zone. Clastic sedimentary fill patterns identified on these isochron maps indicate a combined effect of strike-slip and reverse faulting (i.e., tectonic transpression) produced by active right-lateral shear on the CRFZ, which is consistent with the obliquity of the strike of the fault to the interplate slip vector known from GPS studies in onland Trinidad. The NDRFZ and a sub-parallel and linear family of east-west-striking faults with normal and possibly transtensional motions also contributed to the creation of accommodation space within localized, post-middle Miocene clastic depocenters south of the CRFZ.     

EIDOSCOPE: particle acceleration at plasma boundaries

We describe the mission concept of how ESA can make a major contribution to the Japanese Canadian multi-spacecraft mission SCOPE by adding one cost-effective spacecraft EIDO (Electron and Ion Dynamics Observatory), which has a comprehensive and optimized plasma payload to address the physics of particle acceleration. The combined mission EIDOSCOPE will distinguish amongst and quantify the governing processes of particle acceleration at several important plasma boundaries and their associated boundary layers: collisionless shocks, plasma jet fronts, thin current sheets and turbulent boundary layers. Particle acceleration and associated cross-scale coupling is one of the key outstanding topics to be addressed in the Plasma Universe. The very important science questions that only the combined EIDOSCOPE mission will be able to tackle are: 1) Quantitatively, what are the processes and efficiencies with which both electrons and ions are selectively injected and subsequently accelerated by collisionless shocks? 2) How does small-scale electron and ion acceleration at jet fronts due to kinetic processes couple simultaneously to large scale acceleration due to fluid (MHD) mechanisms? 3) How does multi-scale coupling govern acceleration mechanisms at electron, ion and fluid scales in thin current sheets? 4) How do particle acceleration processes inside turbulent boundary layers depend on turbulence properties at ion/electron scales? EIDO particle instruments are capable of resolving full 3D particle distribution functions in both thermal and suprathermal regimes and at high enough temporal resolution to resolve the relevant scales even in very dynamic plasma processes. The EIDO spin axis is designed to be sun-pointing, allowing EIDO to carry out the most sensitive electric field measurements ever accomplished in the outer magnetosphere. Combined with a nearby SCOPE Far Daughter satellite, EIDO will form a second pair (in addition to SCOPE Mother-Near Daughter) of closely separated satellites that provides the unique capability to measure the 3D electric field with high accuracy and sensitivity. All EIDO instrumentation are state-of-the-art technology with heritage from many recent missions. The EIDOSCOPE orbit will be close to equatorial with apogee 25-30 RE and perigee 8-10 RE. In the course of one year the orbit will cross all the major plasma boundaries in the outer magnetosphere; bow shock, magnetopause and magnetotail current sheets, jet fronts and turbulent boundary layers. EIDO offers excellent cost/benefits for ESA, as for only a fraction of an M-class mission cost ESA can become an integral part of a major multi-agency L-class level mission that addresses outstanding science questions for the benefit of the European science community.     

Identification of minerals and meteoritic materials via Raman techniques after capture in hypervelocity impacts on aerogel

Abstract— Mineral particles analogous to components of cosmic dust were tested to determine if their Raman signatures can be recognized after hypervelocity capture in aerogel. The mineral particles were accelerated onto the silica aerogel by light‐gas‐gun shots. It was found that all the individual minerals captured in aerogel could be identified using Raman (or fluorescence) spectra. The laser beam spot size was ?5 micrometers, and in some cases the captured particles were of a similar small size. In some samples fired into aerogel, a broadening and a shift in the wave numbers of some of the Raman bands was observed, a result of the trapped particles being at elevated temperatures due to laser heating. Temperatures of samples were also estimated from the relative intensities of Stokes and anti‐Stokes Raman bands, or, in the case of corundum particles, from the wave number of fluorescence bands excited by the laser. The temperature varied greatly, dependent upon laser power and the nature of the particle. Most of the mineral particles examined had temperatures below 200 °C at a laser power of about 3 mW at the sample. This temperature is sufficiently low enough not to damage most materials expected to be found captured in aerogel in space. In the worst case, some particles were shown to have temperatures of 500–700 °C. In addition, selected meteorite samples were examined to obtain Raman signatures of their constituent minerals and were then shot into aerogel. It was possible to find Raman signatures after capture in aerogel and obtain a Raman map of a whole grain in situ in the aerogel. It is concluded that Raman analysis is indeed well suited for an in situ analysis of micrometer‐sized materials captured in aerogel.     

Drought, vegetation change, and human history on Rapa Nui (Isla de Pascua, Easter Island)

Stratigraphic records from lake sediment cores and slope deposits on Rapa Nui document prehistoric human impacts and natural environmental changes. A hiatus in sedimentation in Rano Raraku suggests that this lake basin dried out sometime after 4090-4410 cal yr BP and refilled only decades to centuries before AD 1180-1290. Widespread ecosystem changes caused by forest clearance by Polynesian farmers began shortly after the end of this drought. Terrestrial sections show a chronology of burning and soil erosion similar to the lake cores. Although changing sediment types and shifts in the pollen rain suggest that droughts occurred earlier in the Holocene, as yet there is no evidence for droughts occurring after AD 1180-1290. The timing of the agricultural colonization of Rapa Nui now seems well established at ca. AD 1200 and it was accompanied by rapid deforestation that was probably exacerbated by the island's small size, its droughty climate, and the rarity of primeval fires. Detailed records of a large interval of Rapa Nui's ecological history remain elusive due to the drought hiatus in the Rano Raraku sediment record. We find no evidence for a “rat outbreak impact” on Rapa Nui's vegetation preceding anthropogenic forest clearance.     

Post-glacial relative sea level, isostasy, and glacial history in Icy Strait, Southeast Alaska, USA

We use the radiocarbon ages of marine shells and terrestrial vegetation to reconstruct relative sea level (RSL) history in northern Southeast Alaska. RSL fell below its present level around 13,900 cal yr BP, suggesting regional deglaciation was complete by then. RSL stayed at least several meters below modern levels until the mid-Holocene, when it began a fluctuating rise that probably tracked isostatic depression and rebound caused by varying ice loads in nearby Glacier Bay. This fluctuating RSL rise likely reflects the episodic but progressive advance of ice in Glacier Bay that started around 6000 cal yr BP. After that time, RSL low stands probably signaled minor episodes of glacier retreat/thinning that triggered isostatic rebound and land uplift. Progressive, down-fjord advance of the Glacier Bay glacier during the late Holocene is consistent with the main driver of this glacial system being the dynamics of its terminus rather than climate change directly. Only after the glacier reached an exposed position protruding into Icy Strait ca. AD 1750, did its terminus succumb - a century before the climate changes that marked the end of the Little Ice Age - to the catastrophic retreat that triggered the rapid isostatic rebound and RSL fall occurring today in Icy Strait.     

Growth rate of speckled snapper Lutjanus rivulatus (Teleostei: Lutjanidae) based on tag-recapture data from the iSimangaliso Wetland Park,South Africa

The growth rate of speckled snapper Lutjanus rivulatus was investigated using data from a long-term tag-recapture study conducted in the St Lucia Marine Reserve within the iSimangaliso Wetland Park, a World Heritage Site in northern KwaZulu-Natal, South Africa. A total of 1 429 L. rivulatus were tagged and 453 (31.7%) individual fish were recaptured one or more times. Growth rates were modelled from the tag-recapture data using a maximum-likelihood approach. It is shown that L. rivulatus is a slow-growing species with L_∞ = 918?mm FL, K = 0.06 and phi-prime (Ø, the growth index) = 2.69. The effects of deep-hooking and multiple captures were tested and this revealed that there was no significant impact on the growth of L. rivulatus. The growth index was lower than that recorded in many other similar congeneric species. Slow growth, coupled with high levels of residency and site fidelity, suggest that this species is vulnerable to exploitation and that a precautionary approach towards future management is appropriate.     

The ocean response to climate change guides both adaptation and mitigation efforts

The ocean's thermal inertia is a major contributor to irreversible ocean changes exceeding time scales that matter to human society. This fact is a challenge to societies as they prepare for the consequences of climate change, especially with respect to the ocean. Here the authors review the requirements for human actions from the ocean's perspective. In the near term (～2030), goals such as the United Nations Sustainable Development Goals (SDGs) will be critical. Over longer times (～2050–2060 and beyond), global carbon neutrality targets may be met as countries continue to work toward reducing emissions. Both adaptation and mitigation plans need to be fully implemented in the interim, and the Global Ocean Observation System should be sustained so that changes can be continuously monitored. In the longer-term (after ～2060), slow emerging changes such as deep ocean warming and sea level rise are committed to continue even in the scenario where net zero emissions are reached. Thus, climate actions have to extend to time scales of hundreds of years. At these time scales, preparation for “high impact, low probability” risks — such as an abrupt showdown of Atlantic Meridional Overturning Circulation, ecosystem change, or irreversible ice sheet loss — should be fully integrated into long-term planning.摘要在全球变化背景下, 海洋的很多变化在人类社会发展的时间尺度上 (百年至千年) 具有不可逆转性, 海洋巨大的热惯性是造成该不可逆性的主要原因. 这个特征为人类和生态系统应对海洋变化提出一系列挑战. 本文从海洋变化的角度总结了人类应对气候变化的要求, 提出需要进行多时间尺度的规划和统筹. 在近期 (到2030年) , 实现联合国可持续发展目标至关重要. 在中期 (2050–2060年前后) , 全球需要逐步减排并实现碳中和目标. 同时, 适应和减缓气候变化的行动和措施必须同步施行; 全球海洋观测系统需要得以维持并完善以持续监测海洋变化. 在远期 (在2060年之后) , 即使全球达到净零排放, 包括深海变暖和海平面上升在内的海洋变化都将持续, 因此应对全球变化的行动需持续数百年之久. 在该时间尺度, 应对“低概率, 高影响”气候风险 (即发生的可能性较低, 但一旦发生影响极大的事件带来的风险, 例如: 大西洋经圈反转环流突然减弱, 海洋生态系统跨过临界点, 无可挽回的冰盖质量损失等) 的准备应充分纳入长期规划.