Heat flow pattern, base of methane hydrates stability zones and BSRs in Shenhu Area, northern South China Sea

Using the collected 433 heat flow values, we estimated the bases of methane hydrate stability zone (BHSZ), in northern South China Sea (NSCS). Through comparing BHSZs with the depths of bottom simulating reflectors (BSRs), in Shenhu Area (SA), we found that there are big differences between them. In the north of SA, where the water depth is shallow, many slumps developed and the sedimentation rate is high, it appears great negative difference (as large as -192%). However, to the southeast of SA, where the water depth is deeper, sedimentation rate is relatively low and uplift basement topography exists, it changes to positive difference (as large as +45%). The differences change so great, which haven’t been observed in other places of the world. After considering the errors from the process of heat flow measurement, the BSR depth, the relationship of thermal conductivity with the sediments depth, and the fluid flow activities, we conclude that the difference should be not caused by these errors. Such big disagreement may be due to the misunderstanding of BSR. The deviant “BSRs” could represent the paleo-BSRs or just gas-bearing sediment layers, such as unconformities or the specific strata where have different permeability, which are not hydraterelated BSRs.     

九龙江口水体中1995年有机物的转移

1995年3个航次调查研究结果表明,九龙江口水体总有机物的含量受悬浮物含量控制。在S＜5的低盐度区,悬浮泥沙和有机物产生明显的絮凝沉降;在S＞5的广阔海域,它们的迁移接近于理想混合。估算得出九龙江河流的入海通量约：悬浮泥沙为9．8×105t／a;总COD为3．2×104t／a,其中溶解态COD为2.1×104t／a,约占2／3,为水体有机物的主要形态,如换算为溶解有机碳,则DOC的平均通量为3．2×104t／a。     

Air-sea carbon-dioxide flux estimated by eddy covariance method from a buoy observation

Precise measurements of the CO2 gas transfer across the air-sea interface provide a better understanding of the global carbon cycle.The air-sea CO2 fluxes are obtained by the eddy covariance method and the bulk method from a buoy observation in the northern Huanghai sea.The effects of buoy motion on flux calculated by the eddy covariance method are demonstrated.The research shows that a motion correction can improve the correlation coefficient between the CO2 fluxes estimated from two different levels.Without the CO2-H2 O cross-correlation correction which is termed as PKT correction,the air-sea CO2 fluxes estimated by eddy covariance method using the motion corrected data are nearly an order of magnitude larger than those estimated by the bulk method.After the CO2-H2 O cross-correlation correction,some eddy covariance CO2 fluxes indeed become closer to the bulk CO2 flux,whereas some are overcorrected which are in response to small water vapor flux.     

大陆岛入海沉积物通量的估算研究

大陆岛入海沉积物通量（Q_s）信息对于精确解译大陆架沉积记录的研究是个重要补充。针对如何估算大陆岛Q_s的科学问题,本文以中国东南部海域的8 227个大陆岛为例,提出了一种基于邻近大陆中小型河流Q_s的经验公式计算大陆岛Q_s的解决方案。该方案在实施时需设置两个假定,即大陆岛的Q_s法则遵循邻近大陆中小河流的Q_s法则和可将1个大陆岛当作1个河流流域计算其Q_s。结果表明：（1）经验公式计算的大陆岛Q_s为其最小估计值;如考虑大陆岛流域的具体情况,实际的Q_s值会稍微增加,但其增幅不超过n^0.13（n为流域数量）;（2）经验公式能获取大陆岛Q_s的大致数量级信息;大陆岛的总面积为4 418.49 km²,对应Q_s的数量级为10⁶ t/a,与邻近大陆中型河流入海通量的数量级相当;（3）在大河河口湾充填阶段完成以前,大陆岛沉积物是内陆架泥质沉积体的主要物源之一。因此,大陆岛入海沉积物会对大陆架沉积体系的形成和演化造成一定程度的影响,需引起研究人员的高度重视。     

Reevaluation of historical ocean heat content variations with time-varying XBT and MBT depth bias corrections

As reported in former studies, temperature observations obtained by expendable bathythermographs (XBTs) and mechanical bathythermographs (MBTs) appear to have positive biases as much as they affect major climate signals. These biases have not been fully taken into account in previous ocean temperature analyses, which have been widely used to detect global warming signals in the oceans. This report proposes a methodology for directly eliminating the biases from the XBT and MBT observations. In the case of XBT observation, assuming that the positive temperature biases mainly originate from greater depths given by conventional XBT fall-rate equations than the truth, a depth bias equation is constructed by fitting depth differences between XBT data and more accurate oceanographic observations to a linear equation of elapsed time. Such depth bias equations are introduced separately for each year and for each probe type. Uncertainty in the gradient of the linear equation is evaluated using a non-parametric test. The typical depth bias is +10 m at 700 m depth on average, which is probably caused by various indeterminable sources of error in the XBT observations as well as a lack of representativeness in the fall-rate equations adopted so far. Depth biases in MBT are fitted to quadratic equations of depth in a similar manner to the XBT method. Correcting the historical XBT and MBT depth biases by these equations allows a historical ocean temperature analysis to be conducted. In comparison with the previous temperature analysis, large differences are found in the present analysis as follows: the duration of large ocean heat content in the 1970s shortens dramatically, and recent ocean cooling becomes insignificant. The result is also in better agreement with tide gauge observations. On leave from the Meteorological Research Institute of the Japan Meteorological Agency.     

Metal flux as an alternative parameter in evaluating the resource potential for co-rich ferromanganese crusts

We propose a geochemical parameter, “metal flux” in evaluating hydrogenetic Co-rich ferromanganese crust deposits in the Pacific seamount area, that is based on physical, chemical, and geological characterization of the integrated growth piles of crusts. We calculated the metal flux for fifteen sites from different depths ranging between 900-6000m from different seamounts. The secular and areal variations of metal flux indicate a strong geological controls, and also can be a reliable tool for estimating an economic potential of the crusts. The Co flux decreases with increasing water depth, followed by almost constant flux of Ni and Mn. The Al and Fe fluxes vary with regions, indicating higher values in the western regions near the island arc probably related to a supply from the Asian continents. The results imply that Co, a redox sensitive metal element, is controlled by redox conditions of seawater, while Fe and Al are by terrigenous input. The metal flux reflects global and regional conditions and controls the compositional diversity of metals, thus consequently, the parameter can be a reliable powerful tool to estimate or single out more potential areas.     

Spatial variation in shallow sediment methane sources and cycling on the Alaskan Beaufort Sea Shelf/Slope

The MITAS (Methane in the Arctic Shelf/Slope) expedition was conducted during September, 2009 onboard the U.S. Coast Guard Cutter (USCGC) Polar Sea (WAGB-11), on the Alaskan Shelf/Slope of the Beaufort Sea. Expedition goals were to investigate spatial variations in methane source(s), vertical methane flux in shallow sediments (<10 mbsf), and methane contributions to shallow sediment carbon cycling. Three nearshore to offshore transects were conducted across the slope at locations approximately 200 km apart in water column depths from 20 to 2100 m. Shallow sediments were collected by piston cores and vibracores and samples were analyzed for sediment headspace methane (CH₄), porewater sulfate (SO₄²⁻), chloride (Cl⁻), and dissolved inorganic carbon (DIC) concentrations, and CH₄ and DIC stable carbon isotope ratios (δ¹³C). Downward SO₄²⁻ diffusion rates estimated from sediment porewater SO₄²⁻ profiles were between −15.4 and −154.8 mmol m⁻² a⁻¹ and imply a large spatial variation in vertical CH₄ flux between transects in the study region. Lowest inferred CH₄ fluxes were estimated along the easternmost transect. Higher inferred CH₄ flux rates were observed in the western transects. Sediment headspace ${\mathrm{\delta }}^{13}{\text{C}}_{{\text{CH}}_4}$ values ranged from −138 to −48‰, suggesting strong differences in shallow sediment CH₄ cycling within and among sample locations. Measured porewater DIC concentrations ranged from 2.53 mM to 79.39 mM with δ¹³C_DIC values ranging from −36.4‰ to 5.1‰. Higher down-core DIC concentrations were observed to occur with lower δ¹³C where an increase in ${\mathrm{\delta }}^{13}{\text{C}}_{{\text{CH}}_4}$ was measured, indicating locations with active anaerobic oxidation of methane. Shallow core CH₄ production was inferred at the two western most transects (i.e. Thetis Island and Halkett) through observations of low ${\mathrm{\delta }}^{13}{\text{C}}_{{\text{CH}}_4}$ coupled with elevated DIC concentrations. At the easternmost Hammerhead transect and offshore locations, ${\mathrm{\delta }}^{13}{\text{C}}_{{\text{CH}}_4}$ and DIC concentrations were not coupled suggesting less rapid methane cycling. Results from the MITAS expedition represent one of the most comprehensive studies of methane source(s) and vertical methane flux in shallow sediments of the U.S. Alaskan Beaufort Shelf to date and show geospatially variable sediment methane flux that is highly influenced by the local geophysical environment.     

波浪破碎诱导的海-气无机盐通量的参数化

波浪破碎诱导生成的海盐粒子是海洋向大气输运无机盐的主要机制,海气界面的无机盐通量对于全球气候变化有重要影响。本文开展了实验室实验模拟海盐粒子生成实验,定量考察了温度和盐度对海盐粒子中离子质量分布的影响,揭示了初生海盐粒子中各离子的富集和亏损现象与温度和盐度的关系。基于实验室观测分析结果和推测假定,提出了1个既包含海面风速、又反映海表温度和海表盐度影响的海-气无机盐通量参数化方案。将此参数化方案应用于估计海盐粒子向大气输运的各种无机盐离子质量通量,并与传统方法估算结果进行了比对分析。     

The sharp decrease in suspended sediment supply from China's rivers to the sea: anthropogenic and natural causes

Abstract

Based on data from river gauging stations, the multi-year variations in suspended sediment flux (SSF) from China's nine major rivers to the sea were examined. The decadal SSF decreased by 70.2%: from 1.81 Gt/year for 1954–1963 to 0.54 Gt/year for 1996–2005. The decrease in SSF was more dramatic in the arid northern region than in the wet southern region; from north to south, the SSF decreased by 84% in the Yellow River, 42% in the Yangtze River, and 22% in the Pearl River. Dam construction was the principal cause for the decrease in SSF. At present, approximately 2 Gt/year of sediment is trapped in the reservoirs within the nine river basins. Reduced precipitation and increased water extraction and sand mining have also played a role in the decrease in SSF. Although water and sediment conservation programmes have not counteracted the influence of deforestation, they have enhanced the decrease in SSF in recent years. It is concluded that human activity has become a governing factor on riverine sediment delivery to the sea in China.     

Diurnal variability of upper ocean temperature and heat budget in the southern Bay of Bengal during October–November, 1998 (BOBMEX-Pilot)

Time-series data on upper-ocean temperature, Vessel-Mounted Acoustic Doppler Current Profiler (VM-ADCP) measured currents and surface meteorological parameters have been obtained for the first time in the southern Bay of Bengal at 7‡N, 10‡N, and 13‡N locations along 87‡E during October–November, 1998 under BOBMEX-Pilot programme. These data have been analysed to examine the diurnal variability of upper oceanic heat budget and to estimate the eddy diffusivity coefficient of heat in the upper layer. Diurnal variation of near-surface temperature is typical at northern location (13‡N) with a range of 0.5‡C while the diurnal range of temperature is enhanced to 0.8‡C at the central location (10‡N) due to intense solar radiation (1050 W/m²), clear skies and low wind speeds. At the southern location (7‡N), the diurnal variation of temperature is atypical with the minimum temperature occurring at 2000 hrs instead of at early morning hours. In general, the diurnal curve of temperature penetrated up to 15 to 20 m with decreasing diurnal range with depth. The VM-ADCP measured horizontal currents in the upper ocean were predominantly easterly/northeasterly at southern location, north/northerly at central location and northwesterly at northern location, thus describing a large-scale cyclonic gyre with the northward meridional flow along 87‡E. The magnitudes of heat loss at the surface due to air-sea heat exchanges and in the upper 50 m layer due to vertical diffusion of heat are highest at the southern location where intense convective activity followed by overcast skies and synoptic disturbance prevailed in the lower atmosphere. This and the estimated higher value (0.0235 m²/s) of eddy diffusivity coefficient of heat in the upper ocean (0–50 m depth) suggest that 1-D processes controlled the upper layer heat budget at the southern location. On the other hand, during the fair weather conditions, at the central and northern locations, the upper layer gained heat energy, while the sea surface lost (gained) heat energy at northern (central) location. This and lower values of eddy diffusivity coefficient of heat (0.0045 and 0.0150 m²/s) and the northward intensification of horizontal currents at these locations suggest the greater role of horizontal heat advection over the 1-D processes in the upper ocean heat budget at these two locations.