Distribution and sources of organic matter in surficial sediments on the shelf and slope off Tokachi, western North Pacific, inferred from C and N stable isotopes and C / N ratios

Organic carbon (C) and total nitrogen (N) contents and corresponding isotope ratios were determined in surficial sediment (0–3 cm) at 94 stations ranging from 21 to 1995 m water depth off Tokachi, Hokkaido, Japan, to elucidate the distribution and source of sedimentary organic matter. Suspended particulate organic matter (POM) in the seawater and suspended POM and sediment in the Tokachi River were also examined. δ¹³C, δ¹⁵N and C / N ratios of the samples in the Tokachi River suggest that the spring snowmelt is an important process for the transport of terrestrial organic matter to the coastal waters. δ¹³C values of suspended POM in the surface seawater were higher in May and November than in August, while δ¹⁵N values of the POM were higher in May and August than in November. These changes are attributed to seasonal changes in phytoplankton growth rate and nitrate availability. δ¹³C and δ¹⁵N values in the sediments off Tokachi were lowest near the Tokachi River mouth, and increased offshore to constant values that persisted from 134 to 1995 m water depth. The spatial variation in C / N ratios in the sediment mirrored those of δ¹³C and δ¹⁵N. Comparison of δ¹³C, δ¹⁵N and C / N ratios in the sediments off Tokachi with those in the Tokachi River and seawater indicates that about half of the organic matter in the sediment was of terrestrial origin near the Tokachi River mouth, and the sedimentary organic matter from 134 to 1995 m water depth was of marine origin. The organic C content in the sediment was high near the Tokachi River mouth, and also around 1000 m water depth. The C content was significantly correlated with silt plus clay content, with different regression lines for those stations shallower and deeper than 134 m, owing to several stations of higher C content with the elevated C / N ratio on the inner shelf. These results suggest that transport and deposition of organic-rich fine sediment particles by hydrodynamic processes were major factors controlling C content off Tokachi. In addition, the supply of a fraction of terrestrial organic matter with high C / N probably also affected C content on the inner shelf.     

Effect of iron enrichment on the dynamics of transparent exopolymer particles in the western subarctic Pacific

Dynamics of transparent exopolymer particles (TEP) was studied during the first in situ iron-enrichment experiment conducted in the western subarctic Pacific in July–August 2001, with the goal of evaluating the contribution of TEP to vertical flux as a result of increased primary production following iron enrichment in open ocean ecosystems. Subsequent to the enhancement of phytoplankton production, we observed increase in TEP concentration in the surface layer and sedimentation of organic matter beneath it. Vertical profiles of TEP, chlorophyll a (Chl a) and particulate organic carbon (POC) were obtained from six depths between 5 and 70 m, from a station each located inside and outside the enriched patch. TEP and total mass flux were estimated from the floating sediment traps deployed at 200 m depth. Chl a and TEP concentrations outside the patch varied from 0.2 to 1.9 μg L⁻¹ and 40–60 μg XG equiv. L⁻¹, respectively. Inside the patch, Chl a increased drastically from day 7 reaching the peak of 19.2 μg L⁻¹ on day 13, which coincided with the TEP peak of 189 μg XG equiv. L⁻¹. TEP flux in the sediment trap increased from 41 to 88 mg XG equiv. m⁻² d⁻¹, with 8–14% contribution of TEP to total mass flux. This forms the basic data set on ambient concentrations of TEP in the western subarctic Pacific, and evaluation of the effect of iron enrichment on TEP.     

Rising motion of a behind-the-limb flare at 35 GHz

Interferometer observation of a behind-the-limb flare on 7 September, 1977, at 35 GHz ( = 8.6 mm) shows that the microwave non-thermal radio source of the burst is located in the coronal region at the height higher than 7000 km above the photosphere and rises gradually with the velocity of about 30 km s^-1.     

Moisture rainout fraction over the Indian Ocean during austral summer based on $$^{18}\hbox {O}/{}^{16}\hbox {O}$$ ratios of surface seawater,rainwater at latitude range of 10°N–60°S

Oxygen isotope ratios (\(^{18}\hbox {O}/^{16}\hbox {O}\)) of surface seawater and rainwater samples from the Indian Ocean region (10°N–60°S) during austral summer collected onboard ORV Sagar Nidhi during 2011–2013 have been measured along with salinity, sea surface temperature and relative humidity. The rainwater is isotopically lighter (by \(4.6\pm 2.7\permille )\) compared to the equilibrium condensation of the vapour arising from the seawater at the ambient condition. The isotopic composition of the vapour at high altitude responsible for the rain formation at the sampling location is estimated from a global atmospheric water isotope model (IsoGSM2). The apparent deficit of \(\sim \)5\(\permille \) can be explained by invoking a high degree of rainout (on average, about 70% of the overhead atmospheric moisture) during transport of the source vapour to the sampling location undergoing a Rayleigh fractionation. The required rainout fraction is higher (\(\sim \)80%) in the latitude belt 40°–60°S compared to the equatorial belt (\(\sim \)60%). The pattern of variation in the rainout fraction with latitude is consistent with the well-known evaporation/precipitation processes in the Indian Ocean.     

Degradation and dissolution of zooplanktonic organic matter and lipids in early diagenesis

A degradation experiment with zooplankton was carried out to investigate the diagenesis of zooplanktonic organic matter, lipids, and lipid classes. In addition, reactivities and the quantitative relation between bulk organic carbon and waxes (which are the biomarkers of zooplankton) were compared during the experiment to evaluate the possibility of estimating the contributions of zooplanktonic organic matter in organic carbon pools, such as settling particles and surface sediments, from the wax concentration. Lipids were found to be more labile than the bulk organic carbon. Major parts of the organic carbon and lipids which remained on day 120 were found in the particulate fraction, and the accumulations of stable organic carbon and lipids in the dissolved fraction were limited. Although the lipids were more labile than the bulk organic carbon in the early phase of the experiment, the degradation rate of lipids obviously decreased in the subsequent degradation period, demonstrating the presence of stable lipids in zooplankton. Whereas triglycerides readily decreased, phospholipids persisted, making a major contribution to particulate lipids throughout the experiment. Waxes and other structural lipids such as glycolipids were also stably preserved in particulate lipids, suggesting that stable lipids in particulate matter are composed of structural lipids and waxes during early diagenesis. The degradation rate of waxes showed values comparable to that of bulk organic carbon after 11 days of degradation, resulting in constant ratios of waxes/bulk organic carbon (0.8 ± 0.2%, n = 7) during the later incubation period (after 11 days). This result suggests that the ratio could prove useful in evaluating the zooplanktonic organic carbon in organic carbon pools such as surface sediments and settling particulates.     

Oxygen and carbon isotope records of cultured freshwater pearl mussel <Emphasis Type="Italic">Hyriopsis</Emphasis> sp. shell from Lake Kasumigaura,Japan

We present oxygen and carbon isotope ratios and the morphological structure of the cultured freshwater pearl mussel (Hyriopsis sp., Unionidae) shell and pearl. The number of first-order fluctuations of δ¹⁸O of the outer shell layer along the maximum growth axis was consistent with the number of cultured years. The dominant factor controlling annual δ¹⁸O fluctuations was water temperature with a minor contribution from the variation in δ¹⁸O of ambient water, especially during the rainy season. The δ¹³C values were approximately constant throughout the life of the mussel, suggesting that the contributions of body size to δ¹³C of the shell were minor. We observed nine distinct disturbance rings on the outer surface of the shell. Five rings coincided with the five winter peaks of the δ¹⁸O profile, indicating winter growth cessation below approximately 10°C, probably because of either inactive growth at low water temperatures or reproduction. Summer disturbance rings were not observed in all years. Moreover, some summer rings showed discontinuity in the inner structure. These findings suggest that summer growth cessation may be caused by occasional events such as heavy rains, as the decrease of dissolved oxygen concentration. The δ¹⁸O profile and shell structures indicated that shell aragonite was precipitated at close to equilibrium conditions with respect to the oxygen isotope composition of the ambient water. Hyriopsis sp. shells can potentially be used for reconstruction of past hydrologic conditions. The δ¹⁸O of a pearl indicated that calcification occurred over a temperature range of at least 13–23°C. The optimal temperature for pearl calcification in this species is lower than that for marine pearl calcification.     

Mechanism of cyclically polarity reversing solar magnetic cycle as a cosmic dynamo

We briefly describe historical development of the concept of solar dynamo mechanism that generates electric current and magnetic field by plasma flows inside the solar convection zone. The dynamo is the driver of the cyclically polarity reversing solar magnetic cycle. The reversal process can easily and visually be understood in terms of magnetic field line stretching and twisting and folding in three-dimensional space by plasma flows of differential rotation and global convection under influence of Coriolis force. This process gives rise to formation of a series of huge magnetic flux tubes that propagate along iso-rotation surfaces inside the convection zone. Each of these flux tubes produces one solar cycle. We discuss general characteristics of any plasma flows that can generate magnetic field and reverse the polarity of the magnetic field in a rotating body in the Universe. We also mention a list of problems which are currently being disputed concerning the solar dynamo mechanism together with observational evidences that are to be constraints as well as verifications of any solar cycle dynamo theories of short and long term behaviors of the Sun, particularly time variations of its magnetic field, plasma flows, and luminosity.     

prior to surface appearance of sunspot flux tubes and magneto-thermal pulsation of the Sun

We found an evidence that the luminosity of the Sun systematically decreased about 20 days before sunspot surface appearance by analysing time-lag correlation of time derivatives of running mean time profiles of the data of the Active Cavity Radiometer Irradiance Monitor (ACRIM) I experiment on board of Solar Maximum Mission (SMM) and of the data of the daily sunspot number. This indicates that sunspot flux tube cooling and heat transport blocking by the flux tubes start to take place in the interior of the solar convection zone well before the sunspot surface appearance. From this finding and our previous finding that the luminosity of the Sun systematically increased and the blocked heat appeared on the surface about 50 days after the sunspot surface appearance, a new view of sunspot formation and dynamics and a new view of the luminosity modulation emerged. (i) Sunspots of a solar cycle are formed from clusters of flux tubes which can be seen in the running mean time profile of the sunspot number as a peak with duration on the order of 100 to 200 days. (ii) Heat flow is blocked by the cluster of sunspot flux tubes inside the convection zone to decrease the luminosity about 20 days before the surface emergence of the sunspot cluster. (iii) The blocked heat appears on the surface about 50 days after the surface emergence of the cluster of sunspot flux tubes to heat up the surface. This appears as a thermal pulse in the running mean time profile of the ACRIM dat in between the peaks of the sunspot running mean time profile. This process of heating the surface makes the temperature gradient less steep and weakens the buoyancy of sunspot flux tubes below the surface. (vi) The radiative cooling of the surface layer by the excess heat release steepens the temperature gradient so that the buoyancy of the sub-surface magnetic flux tubes becomes stronger to cause the next surge of emergence of a cluster of sunspots and other magnetic activities, which creates a peak in the time profile of the sunspot number. We call this peak a magnetic pulse of the Sun and the coupled process of alternating pulsed appearance of heat and sunspots the magneto-thermal pulsation of the Sun.     

Stable nitrogen isotope composition in sedimentary organic matter as a potential proxy of nitrogen sources for primary producers at a fringing coral reef

The stable nitrogen isotope ratio (δ ¹⁵N) in macroalgae is effectively used as a time-integrated bioindicator to record nitrogen sources for primary producers during their growing periods in aquatic ecosystems. However, the utility of this tool is limited because the occurrence of these organisms is often restricted in space and time. To investigate the potential of chemical composition in sedimentary organic matter (SOM) as a proxy for time-integrated environmental conditions, nitrogen (N) and carbon (C) contents and their stable isotope ratios (δ ¹⁵N and δ ¹³C) were determined, and systematically cross-checked against corresponding values in macroalgae at the Shiraho fringing reef in Okinawa, Japan. Preliminary trials showed that δ ¹⁵N in SOM processed by the “wash-out method” for δ ¹³C analysis yielded similar δ ¹⁵N values to the bulk sediment, despite the loss of some SOM during the process. The amounts of organic matter and the ratio of the HCl-insoluble portion were variable within the reef, probably reflecting local vegetation and subsequent decomposition. The distribution of δ ¹⁵N and δ ¹³C in SOM showed similar trends to those of macroalgae, with mostly constant differences of 1.4‰ and −6.7‰, respectively. These differences throughout the reef appeared to be explained in terms of mixed contributions from macrophyte and epibenthic microalgae growing in different seasons and years, with their debris undergoing diagenetic alteration. Therefore, macroalgae and SOM δ-values can be used in a complementary manner, over various time scales, as indicators of the integrated effect of dissolved inorganic nitrogen (DIN) sources on coral reef ecosystems.     

Effects of the copepod community structure on fecal pellet flux in Kagoshima bay,a deep,semi-enclosed embayment

Seasonal changes in the shape and size composition of fecal pellets were investigated with sediment trap samples from 50 and 150 m in Kagoshima Bay to evaluate how the mesozooplankton community affects fecal pellet flux. Deep vertical mixing was evident in March, and thermal stratification was developed above 50 m in June, August and November. Chlorophyll a, suspended particulate organic carbon (POC) and copepod abundance were uniform throughout the water column during the seasonal mixing and concentrated above 50 m in the stratified seasons. Calanoids were the most predominant copepods in March and poecilostomatoids composed more than 45% of the copepod community in June, August and November. Fecal pellet fluxes at 50 and 150 m were the highest in March, nearly half of POC flux. The relative contribution declined considerably in the other months, especially for less than 4% of POC flux in August. The decline was corresponded to the predominance of cyclopoids and poecilostomatoids. Cylindrical pellets dominated the fecal matters at both depths throughout the study period, while larger cylindrical pellets nearly disappeared at 150 m in June, August and November. Copepod incubation revealed that cylindrical and oval pellets were egested by calanoids and the other copepods, respectively. We suggest that cylindrical fecal pellets produced by calanoid copepods contribute to feces flux but the predominance of poecilostomatoids and/or cyclopoids decreases feces flux via the increase of oval pellets and fragmentation of larger cylindrical pellets.