Seawater carbonate chemistry and community metabolism during an experiment with a coral reef, 2003

The effect of elevated pCO2 on the metabolism of a coral reef community dominated by macroalgae has been investigated utilizing the large 2650 m3 coral reef mesocosm at the Biosphere-2 facility near Tucson, Arizona. The carbonate chemistry of the water was manipulated to simulate present-day and a doubled CO2 future condition. Each experiment consisted of a 1-2 month preconditioning period followed by a 7-9 day observational period. The pCO2 was 404 ± 63 ?atm during the present-day pCO2 experiment and 658 ± 59 ?atm during the elevated pCO2 experiment. Nutrient levels were low and typical of natural reefs waters (NO3? 0.5-0.9 ?M, NH4+ 0.4 ?M, PO43? 0.07-0.09 ?M). The temperature and salinity of the water were held constant at 26.5 ± 0.2°C and 34.4 ± 0.2 ppt. Photosynthetically available irradiance was 10 ± 2 during the present-day experiment and 7.4 ± 0.5 mol photons m?2 d?1 during the elevated pCO2 experiment. The primary producer biomass in the mesocosm was dominated by four species of macroalgae; Haptilon cubense, Amphiroa fragillisima, Gelidiopsis intricata and Chondria dasyphylla. Algal biomass was 10.4 mol C m?2 during the present-day and 8.7 mol C m?2 and during the elevated pCO2 experiments. As previously observed, the increase in pCO2 resulted in a decrease in calcification from 0.041 ± 0.007 to 0.006 ± 0.003 mol CaCO3 m?2 d?1. Net community production (NCP) and dark respiration did not change in response to elevated pCO2. Light respiration measured by a new radiocarbon isotope dilution method exceeded dark respiration by a factor of 1.2 ± 0.3 to 2.1 ± 0.4 on a daily basis and by 2.2 ± 0.6 to 3.9 ± 0.8 on an hourly basis. The 1.8-fold increase with increasing pCO2 indicates that the enhanced respiration in the light was not due to photorespiration. Gross production (GPP) computed as the sum of NCP plus daily respiration (light + dark) increased significantly (0.24 ± 0.03 vs. 0.32 ± 0.04 mol C m?2 d?1). However, the conventional calculation of GPP based on the assumption that respiration in the light proceeds at the same rate as the dark underestimated the true rate of GPP by 41-100% and completely missed the increased rate of carbon cycling due to elevated pCO2. We conclude that under natural, undisturbed, nutrient-limited conditions elevated CO2 depresses calcification, stimulates the rate of turnover of organic carbon, particularly in the light, but has no effect on net organic production. The hypothesis that an increase pCO2 would produce an increase in net production that would counterbalance the effect of decreasing saturation state on calcification is not supported by these data.

Geochemistry of dark-light rhythm sediments of the Japan Sea

Ocean Drilling Program Legs 127 and 128 in the Japan Sea have revealed the existence of numerous dark-light rhythms of remarkable consistency in sediments of late Miocene, latest Pliocene, and especially Pleistocene age. Light-colored units within these rhythms are massive or bioturbated, consist of diatomaceous clays, silty clays, or nannofossil-rich clays, and are generally poor in organic matter. Dark-colored units are homogeneous, laminated, or thinly bedded and include substantial amounts of biogenic material such as well-preserved diatoms, planktonic foraminifers, calcareous nannofossils, and organic matter (maximum 7.4 wt%). The dark-light rhythms show a similar geometrical pattern on three different scales: First-order rhythms consist of a cluster dominated by dark-colored units followed by a cluster dominated by light-colored units (3-5 m). Spectral analysis of a gray-value time series suggests that the frequencies of the first-order rhythms in sediments of latest Pliocene and Pleistocene age correlate to the obliquity and the eccentricity cycles. The second-order dark-light rhythms include a light and a dark-colored unit (10-160 cm). They were formed in time spans of several hundred to several ten thousand years, with variance centering around 10,500 yr. This frequency may correspond to half the precessional cycle. Third-order rhythms appear as laminated or thinly bedded dark-light couplets (2-15 mm) within the dark-colored units of the second-order rhythms and may represent annual frequencies. In interpreting the rhythms, we have to take into account that (1) the occurrence of the first- and second-order rhythms is not necessarily restricted to glacial or interglacial periods as is shown by preliminary stable-isotope analysis and comparison with the published d18O record; (2) they appear to be Milankovitch-controlled; and (3) a significant number of the rhythms are sharply bounded. The origin of the dark-light rhythms is probably related to variations in monsoonal activity in the Japan Sea, which show annual frequencies, but also operates in phase with the orbital cycles.

Magnetic properties of light and dark sediment layers from the Japan Sea

Rock magnetic/paleoclimatic/diagenetic relationships of sediments spanning the last 0.78 Ma have been investigated using samples collected from light and dark layers recovered at ODP Sites 794 (Yamato Basin) and 795 (Japan Basin). Rock-magnetic parameters (K, Kfd, ARM, SIRM, S-ratio) are shown to reflect diagenetic processes and climate-related variations in the concentration, mineralogy and grain-size of the magnetic minerals contained within the sediments. The magnetic mineralogy is dominated by ferrimagnetic (magnetite-type) minerals with a small contribution made by hematite and iron sulphides such as pyrrhotite and/or greigite. Magnetic mineral concentration and grain size vary between light and dark layers with the former characterized by a higher magnetic content and a finer magnetic grain size. Magnetite dissolution, related to sulfate reduction due to bacterial degradation of organic matter, is the process responsible for the magnetic characteristics observed in the dark layers, testifying to the reducing conditions in the basin. Variations in the rock magnetic properties of the sediments are strongly correlated with global oxygen isotope fluctuations, with glacial stages characterized by a lower magnetic mineral content and a coarser magnetic grain size relative to interglacial stages. Major downcore changes in the magnetic properties observed at Site 794 can be related to changes in the oceanographic conditions of the basin associated with the flow of the warm Tsushima Current into the Japan Sea at about 0.35-0.40 Ma ago.

Lacustrine sediments from two setions in northern Greece

We investigated two lignite quarries in northern Greece for orbital and suborbital climate variability. Sections Lava and Vegora are located at the southern and northern boundaries of the Ptolemais Basin, a northwest southeast elongated intramontane basin that contains Upper Miocene to Lower Pliocene lacustrine sediments. Sediments show cyclic alterations of marl-rich (light), and coal-rich or clay-rich (dark) strata on a decimeter to meter scale. First, we established low-resolution ground-truth stratigraphy based on paleomagnetics and biostratigraphy. Accordingly, the lower 67 m and 65 m that were investigated in both sections Vegora and Lava, respectively, belong to the Upper Miocene and cover a time period of 6.85 to 6.57 and 6.46 to 5.98 Ma at sedimentation rates of roughly 14 and 22 cm/ka. In order to obtain a robust and high-resolution chronology, we then tuned carbonate minima (low L* values; high magnetic susceptibility values) to insolation minima. Besides the known dominance of orbital precession and eccentricity, we detected a robust hemi-precessional cycle in most parameters, most likely indicative for monsoonal influence on climate. Moreover, the insolation-forced time series indicate a number of millennial-scale frequencies that are statistically significant with dominant periods of 1.5-8 kyr. Evolutionary spectral analysis indicates that millennial-scale climate variability documented for the Ptolemais Basin resembles the one that is preserved in ice-core records of Greenland. Most cycles show durations of several tens of thousands of years before they diminish or cease. This is surprising because the generally argued cause for Late Quaternary millennial-scale variability is associated with the presence of large ice sheets, which cannot be the case for the Upper Miocene. Possible explanations maybe a direct response to solar forcing, an influence on the formation of North Atlantic Deep Water through the outflow of high-salinity water, or an atmospheric link to the North Atlantic Oscillation.

Varved sediments of the Arabian Sea

The upper Holocene marine section from a kasten core taken from the oxygen minimum zone off Karachi (Pakistan) at water depth 700 m contains continuously laminated sediments with a sedimentation rate of 1.2 mm/yr and a unique record of monsoonal climatic variability covering the past 5000 years. Our chronostratigraphy is based on varve counts verified by conventional and AMS14C dating. Individual hemipelagic varve couplets are about 0.8-1.5 mm thick, with light-colored terrigenous laminae (A) deposited mainly during the winter monsoon alternating with dark-colored laminae (B) rich in marine organic matter, coccoliths, and fish debris that reflect deposition during the high-productivity season of the late summer monsoon (August-October). Precipitation and river runoff appear to control varve thickness and turbidite frequency. We infer that precipitation decreased in the river watershed (indicated by thinning varves) after 3500-4000 yr B.P. This is about the time of increasing aridification in the Near East and Middle East, as documented by decreasing Nile River runoff data and lake-level lowstands between Turkey and northwestern India. This precipitation pattern continued until today with precipitation minima about 2200-1900 yr B.P., 1000 yr B.P., and in the late Middle Ages (700-400 yr B.P.), and precipitation maxima in the intervening periods. As documented by spectral analysis, the thickness of varve couplets responds to the average length of a 250-yr cycle, a 125-yr cycle, the Gleissberg cycle of solar activity (95 yr), and a 56-yr cycle of unknown origin. Higher frequency cycles are also present at 45, 39, 29-31, and 14 yr. The sedimentary gray-value also shows strong variability in the 55-yr band plus a 31-yr cycle. Because high-frequency cyclicity in the ENSO band (ca. 3.5 and 5 yr) is only weakly expressed, our data do not support a straightforward interaction of the Pacific ENSO with the monsoon-driven climate system of the Arabian Sea.

Temperature tolerance of western Baltic Sea Fucus vesiculosus - growth, photosynthesis and survival

Fucus vesiculosus L. (Phaeophyceae) is the most abundant and hence ecologically most important primary producer, carbon sink and habitat provider in the western Baltic Sea. All F. vesiculosus L. specimens were collected on 23 April 2014 from a depth of 0.2-1 m in the non-tidal Kiel Fjord, western Baltic Sea (54°27'N; 10°12'E), where this species forms dense and almost monospecific stands on stones. After sampling the algal thalli were stored in a refrigerator box with water from the sampling site, transported to Bremerhaven and stored at 10 °C for one day in filtered seawater. Experiments were conducted with vegetative apical tips (6.7±0.5 cm length), the actively growing region of F. vesiculosus, which were randomly selected and cut from 144 different individuals prior to the experiments. These tips were acclimated to laboratory conditions for three days in filtered seawater at 10 °C before the start of the experiment. Furthermore, 30 additional vegetative apices were freeze-dried to document the initial biochemical status of F. vesiculosus in its native habitat. A temperature gradient was installed in a walk-in constant cooling chamber (15 °C) in nine water baths (5, 10, 15, 20, 24, 26, 27, 28 and 29 °C ± 0.1 °C) which were tempered by thermostats (5, 10 and 15 °C: Huber Variostat CC + Pilot ONE, Peter Huber Kältemaschinen GmbH, Offenburg, Germany; 20 and 28 °C: Haake DC3, Thermo Fisher Scientific Inc., Waltham, USA; 24, 26, 27 and 29 °C: Haake DC10). Every temperature treatment consisted of four 2 L glass beakers (n = 4). In each beaker four F. vesiculosus apices were grown in 2 µm-filtered North Sea water diluted with demineralized water in a ratio of 1:1 and enriched with nutrients after Provasoli (1968; 1/10 enrichment), leading to a salinity of about 15.6 which equaled habitat conditions. The algae were exposed to an irradiance of 130 µmol photons m-2 s-1 ±10 % (Powerstar HGI-TS 150 W, OSRAM GmbH, Bad Homburg, Germany) measured at the top of the beaker under a 16:8 h L:D cycle. The media in the beakers was changed every third or fourth day and aerated with artificial air containing 380 ppm CO2 (gas mixing device; HTK Hamburg GmbH, Hamburg, Germany). Before the experiment, the algae were acclimated to the final temperatures in steps of 5 °C for 2 days each, beginning at 10 °C. After 21 days exposure time, three out of four samples per replicate were freeze-dried for further biochemical analyses, and afterwards the thermostats were turned off to reduce the temperature to 16±0.4 °C for another 10 days permitting growth under post-culture conditions.

Heavy and light minerals in turbidites from DSDP Hole 19-183, the Aleutian abyssal plain

The Aleutian abyssal plain is a fossil abyssal plain of Paleogene age in the western Gulf of Alaska. The plain is a large, southward-thinning turbidite apron now cut off from sediment sources by the Aleutian Trench. Turbidite sedimentation ceased about 30 m.y. ago, and the apron is now buried under a thick blanket of pelagic deposits. Turbidites of the plain were recovered at site 183 of the Deep Sea Drilling Project on the northern edge of the apron. The heavy-mineral fraction of sand-sized samples is mostly amphibole and epidote with minor pyroxene, garnet, and sphene. The light-mineral fraction is mostly quartzose debris and feldspars. Subordinate lithic fragments consist of roughly equal amounts of metamorphic, plutonic, sedimentary, and volcanic grains. The sand compositions are arkoses in many sandstone classifications, although if fine silt is included with clay as matrix, the sand deposits are feldspathic or lithofeldspathic graywacke. The sands are apparently first-cycle products of deep dissection into a plutonic terrane, and they contrast sharply with arc-derived volcanic sandstones of similar age common on the adjacent North American continental margin. The turbidite sands are stratigraphically remarkably constant in composition, which indicates derivation from virtually the same terrane through a time span approaching 20 m.y. Comparison of Aleutian plain data with the compositions of coeval sedimentary rocks from the northeast Pacific margin shows that the Kodiak shelf area includes possible proximal equivalents of the more distal turbidites. Derivation from the volcaniclastic Mesozoic flysch of the Shumagin-Kodiak shelf is unlikely; more probably the sediments were derived from primary plutonic sources. The turbidites also resemble deposits in the Chugach Mountains and the younger turbidites of the Alaskan abyssal plain and could conceivably have been derived from the coast ranges of southeastern Alaska or western British Columbia. The Aleutian plain sediment most likely was not derived from as far south as the Oregon-Washington continental margin, where coeval sedimentary deposits are dominantly volcaniclastic.

Decreased light availability can amplify negative impacts of ocean acidification on calcifying coral reef organisms

Coral reef organisms are increasingly and simultaneously affected by global and local stressors such as ocean acidification (OA) and reduced light availability. However, knowledge of the interplay between OA and light availability is scarce. We exposed 2 calcifying coral reef species (the scleractinian coral Acropora millepora and the green alga Halimeda opuntia) to combinations of ambient and increased pCO2 (427 and 1073 µatm, respectively), and 2 light intensities (35 and 150 µmol photons/m**2/s) for 16 d. We evaluated the individual and combined effects of these 2 stressors on weight increase, calcification rates, O2 fluxes and chlorophyll a content for the species investigated. Weight increase of A. millepora was significantly reduced by OA (48%) and low light intensity (96%) compared to controls. While OA did not affect coral calcification in the light, it decreased calcification in the dark by 155%, leading to dissolution of the skeleton. H. opuntia weight increase was not affected by OA, but decreased (40%) at low light. OA did not affect algae calcification in the light, but decreased calcification in the dark by 164%, leading to dissolution. Low light significantly reduced gross photosynthesis (56 and 57%), net photosynthesis (62 and 60%) and respiration (43 and 48%) of A. millepora and H. opuntia, respectively. In contrast to A. millepora, H. opuntia significantly increased chlorophyll content by 15% over the course of the experiment. No interactive effects of OA and low light intensity were found on any response variable for either organism. However, A. millepora exhibited additive effects of OA and low light, while H. opuntia was only affected by low light. Thus, this study suggests that negative effects of low light and OA are additive on corals, which may have implications for management of river discharge into coastal coral reefs.

Biosiliceous sedimentation at ODP Site 128-798

Upper Pliocene through Holocene sediments recovered at Site 798 in the Japan Sea (Oki Ridge) exhibit rhythmic variation in weight percent biogenic opal at intervals of ~5 m and periods equivalent to the 41-k.y. obliquity cycle. Variance at 17 and 100 k.y. is observed prior to 1.3 Ma. These cycles are also clearly defined by log data and correspond to clusters of decimeter-scale dark-colored sediment units alternating with clusters of light-colored units. Opal content varies between 3% and 22% between 0 and 1.3 Ma and from 3% to 43% between 1.3 and 2.6 Ma. Long-term opal accumulation rates average 1.8 g/cm**2/k.y. in the late Pliocene/early Pleistocene and decrease by about 60% at ~1.3 Ma. Rough calculations suggest that opal accumulation rates increased and terrigenous flux decreased during the Holocene relative to the last glacial period. Our age control is not yet sufficient to allow a similar analysis of the 41-k.y. cyclicity in opal content throughout the Pleistocene. Stable isotope results from planktonic foraminifers confirm previous suggestions of a strong surface-water freshening event during isotope stage 2; however, this episode appears to be unique during the Pleistocene. Benthic foraminifers are depleted in 18O during parts of glacial stages 2 and 6 relative to adjacent interglacials, suggesting unusual warming and/or freshening of deep waters. Collectively, the stable isotope and %opal data are consistent with continuing isolation of the Japan Sea during the Quaternary with important transitions occurring at 1.3, 0.7 to 1.0, and 0.2 to 0.3 Ma. Complex relationships among the stable isotope results, %opal data, and sediment characteristics such as color and organic and inorganic carbon content preclude development of a simple model to explain cyclical sedimentation. Opal maxima occur within both light and dark intervals and the processes that control surface-water productivity are at times decoupled from the factors that regulate deep-water dysaerobia. We suggest that water column overturn is controlled largely by regional atmospheric circulation that must also have an as yet poorly understood effect on surface-water fertility.