Sediment trap comparison experiments

Four types of sediment traps which are different in their shapes were simultaneously deployed in Funka Bay, Hokkaido or open ocean, in order to compare the quantity and quality of settling particles collected at the same time. In Funka Bay, the larger total particulate fluxes were observed with the sediment traps having the larger height to width ratios. The settling particles collected with the narrower sediment traps were somewhat similar to suspended particle enriched in organic matter, phosphorus and Mn. These results suggest that the narrower sediment trap more effectively collects fine and light particles similar to suspended particles.     

Decomposition of Phytoplankton in Seawater. Part I: Kinetic Analysis of the Effect of Organic Matter Concentration

Decomposition experiments were conducted on cultured phytoplankton (Skeletonema costatum) in seawater containing decomposer and consumer of size less than 500 μm. We determined the decomposition rates of bulk particulate organic matter (POM), the ratio of labile to semi-refractory fractions in the POM, and the POM carbon/ nitrogen (C/N) ratio during decomposition. To identify the kinetic mechanisms involved in the reactions of different order (e.g., first- and second-order), we studied the sensitivity of reaction rates to the initial concentration of POM, ranging from 2.4 to 71 mg-C L⁻¹. The results showed that decomposition consists of two first-order reactions: decomposition of labile and of semi-refractory particulate organic carbon (POC). The decomposition rate constants found for labile (0.13 day⁻¹ at 20°C), and semi-refractory POC (0.008 day⁻¹ at 20°C), and the carbon weight ratio of semi-refractory POC (13% at 20°C), were insensitive to the initial organic matter concentration. The time-dependence of the C/N ratio was also independent of this initial concentration. The decomposition rate constants and the content of semi-refractory POC did not change, regardless of the absence or presence of 25–500 μm organisms in natural seawater. This revised version was published online in July 2006 with corrections to the Cover Date.     

Dynamics of fatty acids in newly biosynthesized phytoplankton cells and seston during a spring bloom off the west coast of Hokkaido Island, Japan

¹³C uptake experiments were carried out at a station off the west coast of Hokkaido Island, Japan, during the period between late winter and spring bloom in 1997. The composition of newly biosynthesized particulate fatty acids was determined using a ¹³C tracer and gas chromatography/mass spectrometry (¹³C GC/MS), and compared with that of particulate matter (seston). Two fatty acid compositional ratios revealed that diatoms biomass (16:1(n−7)/16:0, ∑C₁₆/∑C₁₈) were strikingly high in new cells compared with seston on 17 April, coinciding with the dominance of fucoxanthin. In this study, the Polyunsaturation Index (a measure of the percentage of C₁₆ fatty acids that are polyunsaturated) in new cells is generally close to that in seston, while there was a notable discrepancy between new cells and seston in surface (10 m) waters on 17 April. This large difference between new cells and seston is ascribed to: (1) an increase of newly synthesized storage lipids (mainly 16:0 and 16:1) induced by nitrogen limitation in the top 10 m of the water column; (2) an addition of earlier synthesized phytoplankton cells (high Polyunsaturation Index at logarithmic growth stage) and non-phytoplankton components (detritus and bacteria and zooplankton) into seston. The highest Polyunsaturation Index of C₁₆ fatty acids in seston (33%) occurred at 100 m water depth. This may be caused by “settling planktonic aggregates” or “diatom resting spores”. In the present study, it is reasonable to suggest that the Polyunsaturation Index of C₁₆ fatty acids can be a useful indicator for the ecophysiological state of marine diatom populations.     

Time series of carbonate system variables off Otaru coast in Hokkaido, Japan

We report several biogeochemical parameters (dissolved inorganic carbon (DIC), total alkalinity (TA), dissolved oxygen (DO), phosphate (PO₄), nitrate + nitrite (NO₃ + NO₂), silicate (Si(OH)₄)) in a region off Otaru coast in Hokkaido, Japan on a “weekly” basis during the period of April 2002–May 2003. To better understand the long-term temporal variations of the main factors affecting CO₂ flux in this coastal region and its role as a sink/source of atmospheric CO₂, we constructed an algorithm of DIC and TA using other hydrographic properties. We estimated the CO₂ flux across the air–sea interface by using the classical bulk method. During 1998–2003 in our study region, the estimated fCO_2sea ranged about 185–335 μatm. The maximum of fCO_2sea in the summer was primarily due to the change of water temperature. The minimum of fCO_2sea in the early spring can be explained not only by the change of water temperature but also the change of nutrients and chlorophyll-a. To clarify the factors affecting fCO_2sea (water temperature, salinity, and biological activity), we carried out a sensitivity analysis of these effects on the variation of fCO_2sea. In spring, the biological effect had the largest effect for the minimum of fCO_2sea (40%). In summer, the water temperature effect had the largest effect for the maximum of fCO_2sea (25%). In fall, the water temperature effect had the largest effect for the minimum of fCO_2sea (53%). In winter, the biological effect had the largest effect for the minimum of fCO_2sea (35%).We found that our study region was a sink region of CO₂ throughout a year (−0.78 mol/m²/yr). Furthermore, we estimated that the increase of fCO_2sea was about 0.56 μatm/yr under equilibrium with the atmospheric CO₂ content for the period 1998–2003, with the temporal changes in the variables (T, S, PO₄) on fCO_2sea, thus as the maximum trend of each variable on fCO_2sea was 0.22 μatm/yr, and the trend of residual fCO₂ including gas exchange was 0.34 μatm/yr. This result suggests that interaction among variables would affect gas exchange between air and sea effects on fCO_2sea. We conclude that this study region as a representative coastal region of marginal seas of the North Pacific is special because it was measured, but there is no particular significance in comparison to any other area.     

Silicate correction in the colorimetric determination of phosphate in seawater

An improved Strickland and Parsons' method, in which silicate correction is made, is described for the colorimetric determination of phosphate in seawater. Silicate correction is made by subtracting the value of 0.025 (C/100)², whereC is silicate concentration (µg atoms 1^?1), from the observed phosphate concentration. The relative standard deviations are 2 % at the 1 µg atom PO ₄ ^3? ?Pl^?1 level and less than 1 % at the 3 µg atoms PO ₄ ^3? ?Pl^?1 level in seawater.     

Transport mechanism of suspended matter above the shelf slope at the mouth of Tokyo Bay

Transport mechanism of suspended matter above the shelf slope is investigated with the use of the moorings of time-series sediment trap, current meter and nephelometer at three stations at the mouth of Tokyo Bay, Japan during 21 to 25 August 1993. Tidal pump mechanism is effective for the transport of suspended matter at the shelf edge, but the boring-like flood tidal current resuspends the settled suspended matter, on the bottom of shelf slope and the resuspended matter is resulted to be moved upslope in one tidal cycle at 10 m above the bottom of shelf slope.     

Abiki oscillations in Sakitsu Bay,west Kyushu,Japan

Sakitsu and Yokaku bays in Amakusa in west Kyushu, Japan, experienced inundation damage in the February 2009 meteotsunami (Abiki) event. The oscillation characteristics of both bays are investigated by taking field measurements and conducting numerical experiments with regard to flood mitigation with the aim to reduce the flood impact during Abiki events. A continuous wavelet transform and bandpass filtering both of the pressure and water level indicated that a sequence of pressure disturbances, as small as 1.0 hPa, caused the large amplified oscillation within Sakitsu Bay. When a sequence of ocean long waves entered the bay, a surf beat evolved in the early stages. Subsequently, the sea level began to undergo large amplitude oscillations, and there was a secondary peak of oscillation with a period of around 24 min, as seen in both field measurements and numerical experiments. A surf beat with the period of 12 min formed in Yokaku Bay owing to the continuous incidence of ocean waves with period of 12 min, but its wave period was almost half of that of the natural period of the bay. This surf beat may have entered Sakitsu Bay with natural period of 11.8 min and caused large water-level fluctuations.     

Engineering climate debt: temperature overshoot and peak-shaving as risky subprime mortgage lending

Despite the ambitious temperature goal of the 2015 Paris Agreement, the pace of reducing global CO₂ emissions remains sluggish. This creates conditions in which the idea of temperature ‘overshoot and peak-shaving’ is emerging as a possible strategy to meet the Paris goal. An overshoot and peak-shaving scenario rests upon the ‘temporary’ use of speculative solar radiation management (SRM) technologies combined with large-scale carbon dioxide removal (CDR). Whilst some view optimistically the strategic interdependence between SRM and CDR, we argue that this strategy comes with a risk of escalating ‘climate debt’. We explain our position using the logic of debt and the analogy of subprime mortgage lending. In overshoot and peak-shaving scenarios, the role of CDR and SRM is to compensate for delayed mitigation, placing the world in a double debt: ‘emissions debt’ and ‘temperature debt’. Analogously, this can be understood as a combination of ‘subprime mortgage’ (i.e. large-scale CDR) and ‘home-equity-line-of-credit’ (i.e. temporary SRM). With this analogy, we draw some important lessons from the 2007–2009 US subprime mortgage crisis. The analogy signals that the efficacy of temporary SRM cannot be evaluated in isolation of the feasibility of large-scale CDR and that the failure of the overshoot promise will lead to prolonged peak-shaving, masking an ever-rising climate debt. Overshoot and peak-shaving scenarios should not be presented as a secured feasible investment, but rather as a high-risk speculation betting on insecure promises. Obscuring the riskiness of such scenarios is a precipitous step towards escalating a climate debt crisis.

Key policy insights

• The slow progress of mitigation increases the attraction of an ‘overshoot and peak-shaving’ scenario which combines temporary SRM with large-scale CDR

• Following the logic of debt, the role of CDR and SRM in this scenario is to compensate for delayed mitigation, creating a double debt of CO₂ emissions and global temperature

• Using the analogy of subprime lending, this strategy can be seen as offering a combination of subprime mortgage and open-ended ‘line-of-credit’

• Because the ‘success’ of peak-shaving by temporary SRM hinges critically on the overshoot promise of large-scale CDR, SRM and CDR should not be discussed separately