Yuichiro Kashiyama

Evidence of Global Chlorophyll d

Although analyses of chlorophyll d (Chl d)‐dominated oxygenic photosystems have been conducted since their discovery 12 years ago, Chl d distribution in the environment and quantitative importance for aquatic photosynthesis remain to be investigated. We analyzed the pigment compositions of surface sediments and detected Chl d and its derivatives from diverse aquatic environments. Our data show that the viable habitat for Chl d‐producing phototrophs extends across salinities of 0 to 50 practical salinity units and temperatures of 1� to 40�C, suggesting that Chl d production can be ubiquitously observed in aquatic environments that receive near-infrared light. The relative abundances of Chl d derivatives over that of Chl a derivatives in the studied samples are up to 4%, further suggesting that Chl d‐based photosynthesis plays a quantitatively important role in the aquatic photosynthesis.

Low-diversity shallow marine benthic fauna from the Smithian of northeast Japan: paleoecologic and paleobiogeographic implications

Abstract An unusually low-diversity shallow marine benthic community in a siliciclastic setting was identified and described from the Lower Triassic (Smithian) Hiraiso Formation (Southern Kitakami Mountains, northeast Japan). The Hiraiso fauna includes bivalve species of widespread genera, such as Eumorphotis, Entolium, Bakevellia (Maizuria), Unionites, Neoschizodus, and the oldest record of the crinoid genus Holocrinus. Facies analysis enabled reconstruction of an environmental gradient ranging through storm-dominated sedimentary settings of various depths, thus allowing us to estimate the probable habitats of the shelly fossil assemblage. Regional comparison of contemporaneous shallow marine fossil localities (i.e., Southern Primorye, Maizuru Terrane, and Chichibu Terrane) demonstrated particularly striking similarity among the shallow marine benthic communities of these siliciclastic settings. We thus infer no substantial ecological recovery among these tropical shallow marine benthic communities in Smithian time.

Implications for chloro- and pheopigment synthesis and preservation from combined compound-specific δ 13 C, δ 15 N, and Δ 14 C analysis

Chloropigments and their derivative pheopig- ments preserved in sediments can directly be linked to pho- tosynthesis. Their carbon and nitrogen stable isotopic com- positions have been shown to be a good recorder of recent and past surface ocean environmental conditions tracing the carbon and nitrogen sources and dominant assimilation pro- cesses of the phytoplanktonic community. In this study we report results from combined compound-specific radiocar- bon and stable carbon and nitrogen isotope analysis to exam- ine the time-scales of synthesis and fate of chlorophyll-a and its degradation products pheophytin-a, pyropheophytin-a, and 13 2 ,17 3 -cyclopheophorbide-a-enol until burial in Black Sea core-top sediments. The pigments are mainly of ma- rine phytoplanktonic origin as implied by their stable isotopic compositions. Pigment 15 N values indicate nitrate as the major uptake substrate but 15 N-depletion towards the open marine setting indicates either contribution from N 2-fixation or direct uptake of ammonium from deeper waters. Ra- diocarbon concentrations translate into minimum and max- imum pigment ages of approximately 40 to 1200 years. This implies that protective mechanisms against decomposition such as association with minerals, storage in deltaic anoxic environments, or eutrophication-induced hypoxia and light limitation are much more efficient than previously thought.

Impact of the evolution of carbonate ballasts on marine biogeochemistry in the Mesozoic and associated changes in energy delivery to subsurface waters

Abstract. We have examined the impact of the Mesozoic algal revolution using biogeochemical simulations to analyze the energy flux into the subsurface environment. In particular, the delivery scheme of energy to the subsurface was dramatically altered by the appearance of mineralized exoskeletons, both in algal groups (e.g., coccolithophores) and in zooplanktic taxa. These biominerals, acting as ballast, accentuated the delivery of organic matter to subsurface waters. Thus, the elevated organic carbon flux associated with evolutionary developments in Mesozoic taxa caused an intense but short-lived oceanic euxinia, without an associated mass extinction event, in sharp contrast to the relatively prolonged Paleozoic euxinia that were generally coincident with mass extinctions.