Tropical-cyclone-driven erosion of the terrestrial biosphere from mountains

The transfer of organic carbon from the terrestrial biosphere to the oceans via erosion and riverine transport constitutes an important component of the global carbon cycle. More than one third of this organic carbon flux comes from sediment-laden rivers that drain the mountains in the western Pacific region. This region is prone to tropical cyclones, but their role in sourcing and transferring vegetation and soil is not well constrained. Here we measure particulate organic carbon load and composition in the LiWu River, Taiwan, during cyclone-triggered floods. We correct for fossil particulate organic carbon using radiocarbon, and find that the concentration of particulate organic carbon from vegetation and soils is positively correlated with water discharge. Floods have been shown to carry large amounts of clastic sediment. Non-fossil particulate organic carbon transported at the same time may be buried offshore under high rates of sediment accumulation. We estimate that on decadal timescales, 77–92% of non-fossil particulate organic carbon eroded from the LiWu catchment is transported during large, cyclone-induced floods. We suggest that tropical cyclones, which affect many forested mountains within the Intertropical Convergence Zone, may provide optimum conditions for the delivery and burial of non-fossil particulate organic carbon in the ocean. This carbon transfer is moderated by the frequency, intensity and duration of tropical cyclones

Efficient organic carbon burial in the Bengal fan sustained by the Himalayan erosional system

Author Posting. © Nature Publishing Group, 2007. This is the author's version of the work. It is posted here by permission of Nature Publishing Group for personal use, not for redistribution. The definitive version was published in Nature 450 (2007): 407-410, doi:10.1038/nature06273.Continental erosion controls atmospheric carbon dioxide levels on geological timescales through silicate weathering, riverine transport and subsequent burial of organic carbon in oceanic sediments. The efficiency of organic carbon deposition in sedimentary basins is however limited by the organic carbon load capacity of the sediments and organic carbon oxidation in continental margins. At the global scale, previous studies have suggested that about 70 per cent of riverine organic carbon is returned to the atmosphere, such as in the Amazon basin. Here we present a comprehensive organic carbon budget for the Himalayan erosional system, including source rocks, river sediments and marine sediments buried in the Bengal fan. We show that organic carbon export is controlled by sediment properties, and that oxidative loss is negligible during transport and deposition to the ocean. Our results indicate that 70 to 85 per cent of the organic carbon is recent organic matter captured during transport, which serves as a net sink for atmospheric carbon dioxide. The amount of organic carbon deposited in the Bengal basin represents about 10 to 20 per cent of the total terrestrial organic carbon buried in oceanic sediments. High erosion rates in the Himalayas generate high sedimentation rates and low oxygen availability in the Bay of Bengal that sustain the observed extreme organic carbon burial efficiency. Active orogenic systems generate enhanced physical erosion and the resulting organic carbon burial buffers atmospheric carbon dioxide levels, thereby exerting a negative feedback on climate over geological timescales

Variations in Denitrification and Ventilation Within the Arabian Sea Oxygen Minimum Zone During the Holocene

The continental slope of India is exposed to an intense perennial oxygen minimum zone (OMZ) supporting pelagic denitrification. Sediments that are presently in contact with the lower boundary of the denitrification zone indicate marked changes in the intermediate and bottom waters ventilation of OMZ during the past 9,500 years. The δ15N of sediment suggests that the OMZ waters were less ventilated during the early Holocene (between 9.5 and 8.5 ka BP) resulting in intensified denitrifying conditions with an average δ15N value of 7.8‰, while at the same time stable Mo isotope composition (average δ98Mo of -0.02‰) indicates that the bottom waters that were in contact with the sediments were better oxygenated. By the mid-Holocene OMZ became more oxygenated suppressing denitrification (average δ15N of 6.2‰), while bottom waters gradually became less oxygenated (average δ98Mo of 1.7‰). The mid-Holocene reduction in denitrification coincided with a global decrease in atmospheric N2O as inferred from ice core records, which is consistent with a decreased contribution from the Arabian Sea. Since ~5.5 ka BP OMZ waters have again been undergoing progressive deoxygenation accompanied by increasing denitrification

Anthropogenic perturbation of the carbon fluxes from land to ocean

A substantial amount of the atmospheric carbon taken up on land through photosynthesis and chemical weathering is transported laterally along the aquatic continuum from upland terrestrial ecosystems to the ocean. So far, global carbon budget estimates have implicitly assumed that the transformation and lateral transport of carbon along this aquatic continuum has remained unchanged since pre-industrial times. A synthesis of published work reveals the magnitude of present-day lateral carbon fluxes from land to ocean, and the extent to which human activities have altered these fluxes. We show that anthropogenic perturbation may have increased the flux of carbon to inland waters by as much as 1.0 Pg C yr-1 since pre-industrial times, mainly owing to enhanced carbon export from soils. Most of this additional carbon input to upstream rivers is either emitted back to the atmosphere as carbon dioxide (~0.4 Pg C yr-1) or sequestered in sediments (~0.5 Pg C yr-1) along the continuum of freshwater bodies, estuaries and coastal waters, leaving only a perturbation carbon input of ~0.1 Pg C yr-1 to the open ocean. According to our analysis, terrestrial ecosystems store ~0.9 Pg C yr-1 at present, which is in agreement with results from forest inventories but significantly differs from the figure of 1.5 Pg C yr-1 previously estimated when ignoring changes in lateral carbon fluxes. We suggest that carbon fluxes along the land–ocean aquatic continuum need to be included in global carbon dioxide budgets.Peer reviewe

A revised nitrogen budget for the Arabian Sea

Despite its importance for the global oceanic nitrogen (N) cycle, considerable uncertainties exist about the N fluxes of the Arabian Sea. On the basis of our recent measurements during the German Arabian Sea Process Study as part of the Joint Global Ocean Flux Study (JGOFS) in 1995 and 1997, we present estimates of various N sources and sinks such as atmospheric dry and wet depositions of N aerosols, pelagic denitrification, nitrous oxide (N2O) emissions, and advective N input from the south. Additionally, we estimated the N burial in the deep sea and the sedimentary shelf denitrification. On the basis of our measurements and literature data, the N budget for the Arabian Sea was reassessed. It is dominated by the N loss due to denitrification, which is balanced by the advective input of N from the south. The role of N fixation in the Arabian Sea is still difficult to assess owing to the small database available; however, there are hints that it might be more important than previously thought. Atmospheric N depositions are important on a regional scale during the intermonsoon in the central Arabian Sea; however, they play only a minor role for the overall N cycling. Emissions of N2O and ammonia, deep-sea N burial, and N inputs by rivers and marginal seas (i.e., Persian Gulf and Red Sea) are of minor importance. We found that the magnitude of the sedimentary denitrification at the shelf might be ∼17% of the total denitrification in the Arabian Sea, indicating that the shelf sediments might be of considerably greater importance for the N cycling in the Arabian Sea than previously thought. Sedimentary and pelagic denitrification together demand ∼6% of the estimated particulate organic nitrogen export flux from the photic zone. The main northward transport of N into the Arabian Sea occurs in the intermediate layers, indicating that the N cycle of the Arabian Sea might be sensitive to variations of the intermediate water circulation of the Indian Ocean

Interannuelle Variabilitaet des Partikelflusses im Golf von Bengalen -Forschungsfahrt SO116 Zwischenbericht

From a longterm sediment trap experiment in the Bay of Bengal we could show that sedimentation processes vary interannually and that the individual factors controlling deposition, which are (i) fluvial input, (ii) resuspension of shelf sediments and (iii) monsoon winds are of regionally differing relevance. In contrast to previous assumptions fluxes in the northern Bay of Bengal are not controlled by distance to the Ganges/Brahmaputra mouth only, but by interannual variability of the climatic and hydrographic conditions. Precipitation and discharges of the SE-Indian rivers exert a major influence on the composition of the sinking material during SW monsoon in the central Bay of Bengal. A shift in the plankton community to siliceous species and the increased deposition of lithogenic material result in an increased removal of organic carbon to the deep Bay of Bengal. This indicates that short-term meteorological events can have major implications for the marine carbon cycle. In the southern Bay of Bengal particle flux has a much more pronounced maximum during SW monsoon as in the northern and central parts. A significant reduction of fluxes in the southern Bay of Bengal as a consequence of the Pinatubo eruption and the ENSO event in 1991 delineate the necessity of future studies of the implications of major climatic events on particle fluxes in the northern Indian Ocean. (orig.)SIGLEAvailable from TIB Hannover: F97B2396 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekHamburg Univ. (Germany). Inst. fuer Biogeochemie und Meereschemie (IfBM)DEGerman

Geologiczne konsekwencje reakcji komórki na stres wapniowy

Knowledge on transport and regulation of free calcium in the living cell is used in support of the theory (Kaźmierczak et al. 1985) linking the onset of biocalcification at about the Precambrian/Cambrian boundary to a rise in Ca²⁺ concentrations in the shelf seas to levels toxic to biota. Following this event, fluctuating Ca²⁺ levels in the Phanerozoic seas are supposed to have challenged a variety of protists and invertebrates to respond by depositing no, thin, or thick skeletons respectively. Changes in type and extent of calcification, as observed in the stratigraphical record, are interpreted to reflect the pulsating flow of Ca²⁺ ions through crust, sea, and biota. Some implications of that theory to (i) the history of sea water, (ii) the global carbon cycle, (iii) stable carbon isotope geochemistry, and (iv) sedimentation of suspended clays, are briefly discussed.Ca²⁺ jest jednym z najważniejszych jonów w procesach życiowych, pełniącym, między innymi, różnorakie funkcje jako regulator wewnątrzkomórkowy. Przeciętne stężenie Ca²⁺ w cytoplazmie wynosi 10⁻⁸—10⁻⁷ M i jest zwykle o 4—5 rzędów wielkości niższe od stężeń zewnątrzkomórkowych. Wysokie stężenia jonów wapnia w sąsiedztwie komórki powodują zwiększony napływ Ca²⁺ do cytoplazmy, zagrażający normalnemu funkcjonowaniu organizmu. Do usuwania toksycznego nadmiaru Ca²⁺ z komórki służą różnego rodzaju „pompy jonowe” oraz nośniki białkowe (tzw. kalcyproteiny). Biokalcyfikację można rozpatrywać jako jedną z form detoksykacji wapniowej komórek. Różni się ona od innych sposobów usuwania nadmiaru Ca²⁺ z komórek tym, że w tym przypadku wyprowadzany na nośniku białkowym (glikoproteinowym) wapń jest przy współudziale enzymów (węglanowej anhydrazy lub alkalicznej fosfatazy) neutralizowany do postaci słabo rozpuszczalnej w wodzie soli, której ostateczna forma mineralogiczna zależy od specyficzności wzornika (template) białkowego, na którym epitaksjalnie narastają kryształy. Omówione w pracy dokładniej mechanizmy transportu i regulacji Ca²⁺ w komórce posłużyły do poparcia hipotezy Kaźmierczaka, Ittekkota i Degensa (1985), łączącej powstanie pierwszych struktur szkieletowych na przełomie prekambru i kambru ze wzrostem stężeń Ca²⁺ w szelfowych środowiskach morskich do poziomu toksycznego dla zasiedlających je organizmów. Zgodnie z tą hipotezą, w ciągu fanerozoiku koncentracja Ca²⁺ w morzach szelfowych ulegała wielkoskalowym fluktuacjom, odpowiadającym cyklom regresywno-transgresywnym, sterowanym aktywnością stref ryftowych. Rezultatem tych fluktuacji byłoby okresowe, masowe pojawianie się w prawie wszystkich grupach organizmów morskich form opatrzonych szczególnie masywnymi, wapiennymi lub Ca-fosforanowymi strukturami szkieletowymi. Ca²⁺ w dzisiejszych morzach pochodzi z dwóch głównych źródeł: (1) produktów wietrzenia lądowego, znoszonych wodami rzecznymi i (2) roztworów hydrotermalnych, wydobywających się ze skorupy oceanicznej w strefach ryftowych. Przez większość prekambru usuwanie Ca²⁺ ze środowiska morskiego następowało przede wszystkim przez chemiczne wytrącanie węglanów w strefach pływowych i nadpływowych (np. w formie stromatolitów), lub w pobliżu ryftów. Skład chemiczny wody morskiej w tym czasie zbliżony był do składu dzisiejszych przyryftowych i wulkanicznych jezior sodowych, których wysokie pH (> 10) pozwala utrzymać w roztworze tylko znikome ilości Ca²⁺. Z przejściem od oceanu sodowego do chlorkowego (halitowego), co miało miejsce w ciągu proterozoiku, poziom Ca²⁺ w wodzie morskiej stopniowo wzrastał, szczególnie w zbiornikach epikontynentalnych, zasilanych wraz z postępującą kratonizacją litosfery coraz większymi ilościami Ca²⁺ pochodzącego z wietrzenia kontynentów. Reakcją organizmów na wzrastający stres wapniowy była prawie jednoczesna biokalcyfikacja wielu grup bezkręgowców w wendzie i wczesnym kambrze. „Wymuszenie” przez środowisko wapiennych struktur szkieletowych na organizmach nie było procesem ograniczonym do pogranicza prekambru i kambru. W ciągu fanerozoiku szereg grup organizmów bezszkieletowych odpowiedziało na stres wapniowy swoich środowisk życia wykształceniem wapiennych szkieletów (np. w dewonie otwornice bentosowe, zaś na przełomie triasu i jury planktonowe otwornice i część nannofitoplankterów). Biokalcyfikacja zmieniła generalnie charakter wytrącania węglanów w morzu z chemicznego na enzymatyczny, a ekstrakcja Ca²⁺ w morzach fanerozoicznych stała się prawie wyłącznie domeną organizmów. Wiele pierwotniaków i glonów planktonowych reaguje na stres wapniowy środowiska obfitym wydzielaniem wielocukrów czy glikoprotein kompleksujących Ca²⁺. Obecność tych substancji w wodzie prowadzi z kolei do makroflokulacji drobnych cząstek osadu zawieszonych w wodzie, które bez łączenia się w większe agregaty nie mogłyby opadać na dno. Sedymentacja zawiesiny ilastej jest więc związana z intensywnością wydalniczą planktonu, zależną bezpośrednio od stężenia jonów wapnia (a także innych metali) w środowisku. Praca była częściowo finansowana przez Polską Akademię Nauk w ramach problemu MR II 6