Estimating areal production of intertidal microphytobenthos based on spatio-temporal community dynamics and laboratory measurements

In situ Microphytobenthic community dynamics were combined with laboratory measurement of predominant species by fluorescence methods to estimate the areal primary production. Field investigation of community dynamics of microphytobenthos (MPB) was conducted from August 2006 to August 2007 in intertidal flats of the Nakdong River estuary, Korea. MPB Biomass varied between 0.47 and 16.58 μg cm^?3 in the surface 1 cm sediment, with two dominant diatom species, Amphora coffeaeformis and Navicula sp., occupying average 77.2 ± 14.9% of total number of MPB cells. The biomass was higher in the slightly muddy sand sites than that in the sand site, and showed different pattern of seasonal variation. The profile of vertical distribution of biomass was an exponential decrease trend with depth in sediments. The biomass proportions in the uppermost 3 mm were 57.6% and 37.8% with and without the presence of biofilm, respectively. The two dominant species were cultured in laboratory, and their photosynthetic parameters, rETR_max (relative maximum electron transport rate), α (light utilization coefficient) and E _k (light saturation parameter) were derived from rETR (relative ETR)-irradiance curves by Imaging- PAM (pulse amplitude modulated) fluorometry. The rETR-irradiance curves showed no significant difference of photosynthetic activities between the two species. The areal potential production ranged from 0.74 to 2.22 g C m^?2 d^?1.     

A record of long-time rift activity and earthquake-induced ground effects in Pleistocene deposits of southern Tenerife (Canary Islands,Spain)

Faults with a well-defined strike direction that precisely coincides with the southern rift fault system occur in the study area in southern Tenerife. This fault system was generated contemporaneously with a chain of cinder cones ~948 ka. Open fractures in ignimbrites (~668 ka) and fossil beach deposits (~42 ka) of the El Médano area suggest that the rift-associated fault system was seismically active in the aftermath of the initial volcanic activity (~948 ka) and is probably still active. A second fault system striking perpendicular to the rift-related faults probably originates from a Holocene paleoearthquake of moderate intensity. Earthquake-induced ground effects in fossil beach deposits within the study area are consistent with seismically induced ground effects of several recent and well-documented earthquakes, as well as gravitational sliding triggered by an intense earthquake in the Nicoya Peninsula of Costa Rica in 1990. Both, the rift-associated and the earthquake-induced fault system, initially produced open fractures that were occupied by plants and subsequently stabilized by cementation, forming conspicuous sediment structures in fossil beach deposits of the El Médano site in southern Tenerife.     

Different spreading of Somali and Arabian coastal upwelled waters in the northern Indian Ocean: A case study

The spreading pathways of the Somali and Arabian coastal upwelled waters in the northern Indian Ocean are identified from an ocean re-analysis data set of a single year using numerical passive tracers in a transport model. The Somali and Arabian coastal upwelled waters are found to have entirely different spreading pathways in the northern Indian ocean. The former circulates anticyclonically, is mixed vertically, and is advected to the eastern Indian Ocean along the north equatorial region; while the later intrudes into the northern Arabian Sea, circulates anticyclonically and is advected to the south in the central Arabian Sea and then to the eastern Indian Ocean. The seasonal surface mixing by strong monsoon winds and sheared currents due to dominant eddies of the Somali region are found responsible for mixing 25% of Somali upwelled water with the subsurface and affecting the resultant pathways. The effect of mixing is, however, found negligible in the case of Arabian coastal upwelled water pathways. The seasonal reversal of circulation and eddy dominance during the southwest monsoon cause the Somali upwelled water to spread over the northern Indian Ocean faster than the simultaneously upwelled Arabian coastal water.     

Comparison of the effects of short-term UVB radiation exposure on phytoplankton photosynthesis in the temperate Changjiang and subtropical Zhujiang estuaries of China

We examined the effect of solar ultraviolet radiation B (UVB, 280–315 nm) on photosynthesis of natural phytoplankton assemblages in the temperate Changjiang River Estuary (CRE) in the East China Sea (ECS), and the subtropical Zhujiang River Estuary (ZRE) in the South China Sea (SCS) from August 2002 to April 2003. The short-term effect of UVB was assessed by exposing samples in quartz tubes/bottles to solar radiation under three treatments: (1) natural sunlight (NS) with UVB (NS-UVB); (2) photosynthetically active radiation (PAR, NS cut off UVB); and (3) NS with additional artificial UVB (NS + A-UVB). Solar UVB apparently inhibited phytoplankton photosynthesis rates. In the temperate CRE-ECS, solar UVB reduced surface phytoplankton photosynthesis by about 28% in August and February, while in the subtropical ZRE-SCS the inhibition was only 22% in September and October. In the CRE-ECS, phytoplankton in the stratified water column displayed stronger UVB inhibition when deeper water samples were exposed to surface UVB. Phytoplankton in the mixed water column did not show strong UVB inhibition, while light shift exposure of deeper phytoplankton in the same water column to surface light produced similar results, indicating that mixing moderates UVB effects. In the ZRE-SCS, surface phytoplankton showed greater photoinhibition in January (sunny). However, in April (cloudy), phytoplankton showed little UVB inhibition. Incubation for a short time without UVB showed a large increase in Chl a at two stations in the ZRE-SCS, but a large decrease at the other station in the presence of UVB. In contrast, in the CRE-ECS, a similar incubation experiment without UVB showed a decrease in Chl a, and small UVB inhibition of Chl a at two stations. Nutrient conditions might have played a role in the difference of UVB inhibition between the two regions as the ZRESCS had relatively high concentrations of all nutrients while PO₄ was only 0.21 μM at one of the CRE-ECS stations. The results suggest that phytoplankton in temperate waters would be more responsive to variation of UVB than ones in subtropical waters.     

Rare earth elements in bottom sediments of major rivers around the Yellow Sea: implications for sediment provenance

Rare earth elements (REEs) of 91 fine-grained bottom sediment samples from five major rivers in Korea (the Han, Keum, and Yeongsan) and China (the Changjiang and Huanghe) were studied to investigate their potential as source indicator for Yellow Sea shelf sediments, this being the first synthetic report on REE trends for bottom sediments of these rivers. The results show distinct differences in REE contents and their upper continental crust (UCC)-normalized patterns: compared to heavy rare earth elements (HREEs), light rare earth elements (LREEs) are highly enriched in Korean river sediments, in contrast to Chinese river sediments that have a characteristic positive Eu anomaly. This phenomenon is observed also in primary source rocks within the river catchments. This suggests that source rock composition is the primary control on the REE signatures of these river sediments, due largely to variations in the levels of chlorite and monazite, which are more abundant in Korean bottom river sediments. Systematic variations in ΣLREE/ΣHREE ratios, and in (La/Yb)–(Gd/Yb)_UCC but also (La/Lu)–(La/Y)_UCC and (La/Y)–(Gd/Lu)_UCC relations have the greatest discriminatory power. These findings are consistent with, but considerably expand on the limited datasets available to date for suspended sediments. Evidently, the REE fingerprints of these river sediments can serve as a useful diagnostic tool for tracing the provenance of sediments in the Yellow Sea, and for reconstructing their dispersal patterns and the circulation system of the modern shelf, as well as the paleoenvironmental record of this and adjoining marginal seas.     

Late Pleistocene to Holocene sedimentation and hydrocarbon seeps on the continental shelf of a steep,tectonically active margin,southern California,USA

Small, steep, uplifting coastal watersheds are prolific sediment producers that contribute significantly to the global marine sediment budget. This study illustrates how sedimentation evolves in one such system where the continental shelf is largely sediment-starved, with most terrestrial sediment bypassing the shelf in favor of deposition in deeper basins. The Santa Barbara–Ventura coast of southern California, USA, is considered a classic area for the study of active tectonics and of Tertiary and Quaternary climatic evolution, interpretations of which depend upon an understanding of sedimentation patterns. High-resolution seismic-reflection data over >570 km² of this shelf show that sediment production is concentrated in a few drainage basins, with the Ventura and Santa Clara River deltas containing most of the upper Pleistocene to Holocene sediment on the shelf. Away from those deltas, the major factor controlling shelf sedimentation is the interaction of wave energy with coastline geometry. Depocenters containing sediment 5–20 m thick exist opposite broad coastal embayments, whereas relict material (bedrock below a regional unconformity) is exposed at the sea floor in areas of the shelf opposite coastal headlands. Locally, natural hydrocarbon seeps interact with sediment deposition either to produce elevated tar-and-sediment mounds or as gas plumes that hinder sediment settling. As much as 80% of fluvial sediment delivered by the Ventura and Santa Clara Rivers is transported off the shelf (some into the Santa Barbara Basin and some into the Santa Monica Basin via Hueneme Canyon), leaving a shelf with relatively little recent sediment accumulation. Understanding factors that control large-scale sediment dispersal along a rapidly uplifting coast that produces substantial quantities of sediment has implications for interpreting the ancient stratigraphic record of active and transform continental margins, and for inferring the distribution of hydrocarbon resources in relict shelf deposits.     

Observation of the bottom boundary layer off the Soya Warm Current

A mooring observation of current velocity, temperature and bottom pressure was carried out approximately 30 km off the coast of Monbetsu, between August 7 and September 2, 2005, to investigate the characteristics of bottom boundary layer (BBL) off the Soya Warm Current (SWC). We succeeded in measuring the Ekman veering and bottom Ekman transport in the BBL. On comparing the observed current velocity with that represented by the classical theoretical equation, the observed alongshore current velocity in BBL disagreed with that represented by the classical theoretical equation, but the cross-shore one agreed well. However after applying a linear extrapolation for the alongshore current velocity to estimate the alongshore geostrophic current velocity above the bottom, we could explain the alongshore current velocity by that represented in the classical theoretical equation. Consequently, our observations strongly support one of the proposed formation mechanisms of the cold-water belt observed off the SWC, that is, the convergence of bottom Ekman transport. The volume transport of vertical pumping velocity was estimated to be (0.12–0.25) Sv. In addition, the vertical profile of average temperature in all observation periods shows that slightly warmer water lies beneath the homogenous temperature layer, in the BBL. The result is considered to imply that the down-slope advection due to bottom Ekman transport supplies the SWC water in BBL and the eddy diffusivity of order of 10⁻³ m²s⁻¹ maintains the oceanic structure in the bottom mixed layer.     

Diatoms grow faster using ammonium in rapidly flushed eutrophic Dokai Bay,Japan

The importance of the nitrogen source for phytoplankton growth in a highly eutrophic embayment, Dokai Bay, was investigated. The DIN concentration often exceeded 100 μM of which 40–70% was NH₄ ⁺. During two incubation experiments, the natural assemblage of mainly diatoms took up NH₄ ⁺ instead of NO₃ ⁻. The growth of two Skeletonema species isolated in Dokai Bay were significantly faster on NH₄ ⁺ (1.86 and 1.27 div. d⁻¹ respectively) than on NO₃ ⁻ (1.55 and 1.04 div. d⁻¹ respectively). Our results indicated that these diatoms could grow faster by using NH₄ ⁺ compared to NO₃ ⁻ in this eutrophic bay.     

苏皖下扬子区晚白垩世以来的构造-热历史：浦口组砂岩磷灰石裂变径迹证据

对苏皖下扬子区上白垩统浦口组（K2P）的三个砂岩样品进行了磷灰石裂变径迹（AFT）研究。结果显示：2个样品的AFT合并年龄为（88．8±4．4）Ma（径迹长度为（12．0±0．3）μm）和（82．1±6．8）Ma（径迹长度为（14．4±0．3）μm）与浦口组沉积年龄相近,说明它们沉降的幅度达到但没有超过AFT部分退火区间,1个样品的AFT合并年龄（117．3±5．9）Ma（径迹长度为（13．3±0．3）μm）大于浦口组沉积年龄,代表物源区抬升、剥露的冷却年龄。根据热历史模拟结果,识别出黄桥事件（110～90Ma）、仪征事件（70～60Ma）和三垛事件（35～22Ma）三期重要的构造事件,并将下扬子区晚白垩世以来的盆地演化划分为四个阶段：110～70Ma断坳复合型伸展盆地、70～35Ma拉张断陷盆地、35～22Ma挤压抬升阶段和22Ma至今坳陷盆地。     

Mixed layer depth climatology of the North Pacific based on Argo observations

A monthly mean climatology of the mixed layer depth (MLD) in the North Pacific has been produced by using Argo observations. The optimum method and parameter for evaluating the MLD from the Argo data are statistically determined. The MLD and its properties from each density profile were calculated with the method and parameter. The monthly mean climatology of the MLD is computed on a 2° × 2° grid with more than 30 profiles for each grid. Two bands of deep mixed layer with more than 200 m depth are found to the north and south of the Kuroshio Extension in the winter climatology, which cannot be reproduced in some previous climatologies. Early shoaling of the winter mixed layer between 20–30°N, which has been pointed out by previous studies, is also well recognized. A notable feature suggested by our climatology is that the deepest mixed layer tends to occur about one month before the mixed layer density peaks in the middle latitudes, especially in the western region, while they tend to coincide with each other in higher latitudes.