Malaspina 2010: observaciones de R/ETS

[EN]Respiratory electron transport system (ETS) activities have been used, in the past, to study respiration in many marine organisms and many different environments. The methodology follows standard practices of enzymology, by attempting to measure the maximum velocity of the enzyme reaction (Vmax) sensu Michaelis-Menten. Under controlled conditions of nutritional state the ETS method is well correlated with in situ respiration. In the interdisciplinary Expedition MALASPINA 2010, that circumnavigated the planet, we had the chance in three of seven transects (Cape Town to Perth; Perth to Sydney and Cartagena de Indias to Cartagena) to take zooplankton samples from the southern Indian Ocean and from North Atlantic Ocean. From these samples we measured protein and 150 ratios between in vivo respiration and potential respiration (ETS activity) in three size-classes of zooplankton between 100?m to > 1000?m, in the upper 150 meters of the water column. Normally, the measurements were made on fresh naturally nourished zooplankton (in situ). When biomass permitted, measurements were also made on zooplankton starved for 24 h. With this data we are investigating the variations in the R/ETS ratio and Kleiber?s law under different nutritional conditions, different oceanographic conditions, and different oceanographic regions. This analysis will help our ongoing investigation of ETS activity as an index of both respiration and of living biomass. The information acquired will facilitate the calculation of zooplankton respiration for some relatively unexplored areas of the Indian and Atlantic oceans. This data will then be available for integration with results of other Malaspina research programs

Changes of the surface cell of the Atlantic and Indian Meridional overturning circulations

Premio Extraordinario de Doctorado. Rama de Ciencias.

Maremoti in bacini limitati

The work of my thesis is focused on the impact of tsunami waves in limited basins. By limited basins I mean here those basins capable of modifying significantly the tsunami signal with respect to the surrounding open sea. Based on this definition, we consider limited basins not only harbours but also straits, channels, seamounts and oceanic shelves. I have considered two different examples, one dealing with the Seychelles Island platform in the Indian Ocean, the second focussing on the Messina Strait and the harbour of the Messina city itself (Italy). The Seychelles platform is differentiated at bathymetric level from the surrounding ocean, with rapid changes from 2 km to 70 meters over short horizontal distances. The study of the platform response to the tsunami propagation is based on the simulation of the mega-event occurred on 26 December 2004. Based on a hypothesis for the earthquake causative fault, the ensuing tsunami has been numerically simulated. I analysed synthetic tide gauge records at several virtual tide gauges aligned along the direction going from the source to the platform. A substantial uniformity of tsunami signals in all calculated open ocean tide-gauge records is observed, while the signals calculated in two points of the Seychelles platform show different features both in terms of amplitude and period of the perturbation. To better understand the content in frequency of different calculated marigrams, a spectral analysis was carried out. In particular the ratio between the calculated tide-gauge records spectrum on the platform and the average tide-gauge records in the open ocean was considered. The main result is that, while in the average spectrum in the open ocean the fundamental peak is related to the source, the platform introduces further peaks linked both to the bathymetric configuration and to coastal geometry. The Messina Strait represents an interesting case because it consists in a sort of a channel open both in the north and in the south and furthermore contains the limited basin of the Messina harbour. In this case the study has been carried out in a different way with respect to the Seychelles case. The basin was forced along a boundary of the computational domain with sinusoidal functions having different periods within the typical tsunami frequencies. The tsunami has been simulated numerically and in particular the tide-gauge records were calculated for every forcing function in different points both externally and internally of the channel and of the Messina harbour. Apart from the tide-gauge records in the source region that almost immediately reach stationarity, all the computed signals in the channel and in the Messina harbour present a transient variable amplitude followed by a stationary part. Based exclusively on this last part, I calculated the amplification curves for each site. I found that the maximum amplification is obtained for forcing periods of approximately 10 minutes.

PBDEs in the atmosphere over the Asian marginal seas, and the Indian and Atlantic oceans

Air samples were collected from Jan 16 to Mar 14, 2008 onboard the Oceanic II- The Scholar Ship which navigated an east–west transect from Shanghai to Cape Verde, and polybrominated diphenyl ethers (PBDEs) were analyzed in these samples. PBDE concentrations in the atmosphere over the open seas were influenced by proximity to source areas and land, and air mass origins. The concentrations of Σ21PBDEs over the East and South China Seas, the Bay of Bengal and the Andaman Sea, the Indian Ocean, and the Atlantic Ocean were 10.8 ± 6.13, 3.22 ± 1.57, 5.12 ± 3.56, and 2.87 ± 1.81 pg m−3, respectively. BDE-47 and -99 were the dominant congeners in all the samples, suggesting that the widely used commercial penta-BDE products were the original sources. Over some parts of Atlantic and Indian Ocean, daytime concentrations of BDE-47 and BDE-99 were higher than the concentrations at night. The strong atmospheric variability does not always coincide with a diurnal cycle, but the variability in air concentrations in such remote areas of the ocean remains strong. No significant trends were found for each of PBDE congener with latitude.

North-south palaeohydrological contrasts in the central Mediterranean during the Holocene: tentative synthesis and working hypotheses

On the basis of a multi-proxy approach and a strategy combining lacustrine and marine records along a north–south transect, data collected in the central Mediterranean within the framework of a collaborative project have led to reconstruction of high-resolution and well-dated palaeohydrological records and to assessment of their spatial and temporal coherency. Contrasting patterns of palaeohydrological changes have been evidenced in the central Mediterranean: south (north) of around 40° N of latitude, the middle part of the Holocene was characterised by lake-level maxima (minima), during an interval dated to ca. 10 300–4500 cal BP to the south and 9000–4500 cal BP to the north. Available data suggest that these contrasting palaeohydrological patterns operated throughout the Holocene, both on millennial and centennial scales. Regarding precipitation seasonality, maximum humidity in the central Mediterranean during the middle part of the Holocene was characterised by humid winters and dry summers north of ca. 40° N, and humid winters and summers south of ca. 40° N. This may explain an apparent conflict between palaeoclimatic records depending on the proxies used for reconstruction as well as the synchronous expansion of tree species taxa with contrasting climatic requirements. In addition, south of ca. 40° N, the first millennium of the Holocene was characterised by very dry climatic conditions not only in the eastern, but also in the central- and the western Mediterranean zones as reflected by low lake levels and delayed reforestation. These results suggest that, in addition to the influence of the Nile discharge reinforced by the African monsoon, the deposition of Sapropel 1 has been favoured (1) by an increase in winter precipitation in the northern Mediterranean borderlands, and (2) by an increase in winter and summer precipitation in the southern Mediterranean area. The climate reversal following the Holocene climate optimum appears to have been punctuated by two major climate changes around 7500 and 4500 cal BP. In the central Mediterranean, the Holocene palaeohydrological changes developed in response to a combination of orbital, ice-sheet and solar forcing factors. The maximum humidity interval in the south-central Mediterranean started ca. 10 300 cal BP, in correlation with the decline (1) of the possible blocking effects of the North Atlantic anticyclone linked to maximum insolation, and/or (2) of the influence of the remnant ice sheets and fresh water forcing in the North Atlantic Ocean. In the north-central Mediterranean, the lake-level minimum interval began only around 9000 cal BP when the Fennoscandian ice sheet disappeared and a prevailing positive NAO-(North Atlantic Oscillation) type circulation developed in the North Atlantic area. The major palaeohydrological oscillation around 4500–4000 cal BP may be a non-linear response to the gradual decrease in insolation, with additional key seasonal and interhemispheric changes. On a centennial scale, the successive climatic events which punctuated the entire Holocene in the central Mediterranean coincided with cooling events associated with deglacial outbursts in the North Atlantic area and decreases in solar activity during the interval 11 700–7000 cal BP, and to a possible combination of NAO-type circulation and solar forcing since ca. 7000 cal BP onwards. Thus, regarding the centennial-scale climatic oscillations, the Mediterranean Basin appears to have been strongly linked to the North Atlantic area and affected by solar activity over the entire Holocene. In addition to model experiments, a better understanding of forcing factors and past atmospheric circulation patterns behind the Holocene palaeohydrological changes in the Mediterranean area will require further investigation to establish additional high-resolution and well-dated records in selected locations around the Mediterranean Basin and in adjacent regions. Special attention should be paid to greater precision in the reconstruction, on millennial and centennial timescales, of changes in the latitudinal location of the limit between the northern and southern palaeohydrological Mediterranean sectors, depending on (1) the intensity and/or characteristics of climatic periods/oscillations (e.g. Holocene thermal maximum versus Neoglacial, as well as, for instance, the 8.2 ka event versus the 4 ka event or the Little Ice Age); and (2) on varying geographical conditions from the western to the eastern Mediterranean areas (longitudinal gradients). Finally, on the basis of projects using strategically located study sites, there is a need to explore possible influences of other general atmospheric circulation patterns than NAO, such as the East Atlantic–West Russian or North Sea–Caspian patterns, in explaining the apparent complexity of palaeoclimatic (palaeohydrological) Holocene records from the Mediterranean area.

Satellite-Detected Fluorescence Reveals Global Physiology of Ocean Phytoplankton

Phytoplankton photosynthesis links global ocean biology and climate-driven fluctuations in the physical environment. These interactions are largely expressed through changes in phytoplankton physiology, but physiological status has proven extremely challenging to characterize globally. Phytoplankton fluorescence does provide a rich source of physiological information long exploited in laboratory and field studies, and is now observed from space. Here we evaluate the physiological underpinnings of global variations in satellite-based phytoplankton chlorophyll fluorescence. The three dominant factors influencing fluorescence distributions are chlorophyll concentration, pigment packaging effects on light absorption, and light-dependent energy-quenching processes. After accounting for these three factors, resultant global distributions of quenching-corrected fluorescence quantum yields reveal a striking consistency with anticipated patterns of iron availability. High fluorescence quantum yields are typically found in low iron waters, while low quantum yields dominate regions where other environmental factors are most limiting to phytoplankton growth. Specific properties of photosynthetic membranes are discussed that provide a mechanistic view linking iron stress to satellite-detected fluorescence. Our results present satellite-based fluorescence as a valuable tool for evaluating nutrient stress predictions in ocean ecosystem models and give the first synoptic observational evidence that iron plays an important role in seasonal phytoplankton dynamics of the Indian Ocean. Satellite fluorescence may also provide a path for monitoring climate-phytoplankton physiology interactions and improving descriptions of phytoplankton light use efficiencies in ocean productivity models.

Noble metal abundances in ODP Leg 115 basalts (Table 1)

A comparison of 50 basalts recovered at Sites 706, 707, 713, and 715 along the Reunion hotspot trace during Ocean Drilling Program Leg 115 in the Indian Ocean shows that seafloor alteration had little effect on noble metal concentrations (Au, Pd, Pt, Rh, Ru, and Ir), determined by inductively coupled plasma-mass spectrometry (ICP-MS), which generally tend to decrease with magma evolution. Their compatible-element behavior may be related to the precipitation of Ir-Os-based alloys, chromite, sulfides, and/or olivine and clinopyroxene in some combination. The simplest explanation indicates silicate control of concentrations during differentiation. Basalts from the different sites show varying degrees of alkalinity. Noble metal abundances tend to increase with decreasing basalt alkalinity (i.e., with increasing percentages of mantle melting), indicating that the metals behave as compatible elements during mantle melting. The retention of low-melting-point Au, Pd, and Rh in mantle sulfides, which mostly dissolve before significant proportions of Ir-Os-based alloys melt, explains increasing Pd/Ir ratios with decreasing alkalinity (increasing melting percentages) in oceanic basalts. High noble metal concentrations in Indian Ocean basalts (weighted averages of Au, Pd, Rh, Pt, Ru, and Ir in Leg 115 basalts are 3.2, 8.1, 0.31, 7.3, 0.22, and 0.11 ppb, respectively), compared with basalts from some other ocean basins, may reflect fundamental primary variations in upper- mantle noble metal abundances

Isotope ratios of basalts from ODP Leg 115 holes (Table 1)

Strontium, neodymium, and lead isotope ratios are reported for 13 Leg 115 basalts as well as 3 basalts from Texaco drill hole SM-1 on the Mascarene Plateau. The 87Sr/86Sr ratios and eNd range from 0.70330 to 0.70439 and 5.5 to 7.4, respectively, although 87Sr/86Sr ratios higher than 0.70383 are found only in SM-1 basalts. The high 87Sr/86Sr values are thought to reflect seawater Sr in secondary phases, although all samples were strongly leached in HC1 before analysis. 206Pb/204Pb ratios range from 18.53 to 18.80, and sho high 207Pb/204Pb and 208Pb/204Pb ratios relative to 206Pb/204Pb ratios, typical of Indian Ocean mid-ocean ridge (MORB) and oceanic-island basalts (OIB). Isotopic compositions of Leg 115 basalts generally fall between fields for MORB and Reunion Island basalts, consistent with the conclusion drawn from geochronological studies that Deccan flood basalt volcanism, the Chagos-Laccadive Ridge, and the Mascarene Plateau are all products of the Reunion mantle plume. Isotopic compositions of magmas produced by this plume have varied systematically with time in the direction of less "depleted," less MORB-like isotopic signatures. This compositional change has been accompanied by a decrease in eruption rate. We interpret Deccan volcanism as the voluminous beginning of the plume. Reduced entrainment of asthenosphere following melting of the plume head resulted in less MORB-like isotope ratios in magmas and a decrease in eruptive activity with time.

Paleomagnetic of basalts from the Kerguelen Plateau

Paleomagnetic measurements were performed on 106 basalt samples collected from Holes 747C, 748C, 749C, and 750B. Basalt samples were recovered from the southern portion of the Kerguelen Plateau and the transitional zone between the northern and southern plateau in the south central Indian Ocean. The ages of basalts range from 100 to 115 Ma. In addition to the preliminary shipboard measurements (Schlich, Wise, et al., 1989, doi:10.2973/odp.proc.ir.120.1989), characteristic inclinations of the magnetization were obtained using mainly stepwise thermal demagnetization of the samples. Reliable paleomagnetic results were obtained from three sites (Sites 747, 748, and 749). The paleomagnetic inclinations of Sites 747, 748, and 749 are -51°, -63°, and -62°, respectively. The considerable differences between the paleomagnetic and present inclinations of about 70° at Sites 747, 748, and 749 indicate that displacement in the direction of the geomagnetic meridian has taken place since formation of the basalt. Shallower paleomagnetic inclinations than the present inclinations at each site imply a southward movement of the sites with respect to the geomagnetic pole. By comparing the apparent polar wander path of Antarctica with the virtual geomagnetic pole (VGP) of the Southern Kerguelen Plateau, we have concluded that no major tectonic movement has taken place between the Kerguelen Plateau and Antarctica since formation of the basalt (i.e., 100-115 Ma). The angular dispersion of the VGP for the Kerguelen Plateau is calculated as 17°.

Planktonic foraminiferal biostratigraphy and stable carbon isotope ratios of late middle Eocene sediments from Blake Plateau, West Atlantic Ocean

The muricate planktonic foraminiferal genera Morozovella and Acarinina were abundant and diverse during the upper Palaeocene to middle Eocene and dominated the tropical and subtropical assemblages. A significant biotic turnover in planktonic foraminifera occurred in the latest middle Eocene with a notable reduction in the acarininid lineage and the extinction of the morozovellids. These genera are extensively employed as palaeoclimatic and biostratigraphic markers and, therefore, this turnover episode is an important event in the record of the Cenozoic planktonic foraminifera. Sediments from the western North Atlantic (Ocean Drilling Program Site 1052) were examined in order to investigate these extinction events, in terms of both timing and mechanisms. Biostratigraphic events of the middle and late Eocene have been examined with a sampling resoluti on of approximately 3 kyr. These have been calibrated to the magneto- and astrochronology to accurately define the timing of key biostratigraphic events, particularly the extinction of Morozovella spinulosa which is a distinct biomarker for late middle Eocene sediments. High-resolution biostratigraphy reveals that the extinctions in the muricate group occurred in a stepwise form. The large acarininids (Acarinina praetopilensis) terminate 10 kyr prior to the extinction of M. spinulosa and small acarininids (Acarinina medizzai and Acarinina echinata) continue into the upper Eocene. High-resolution stable isotope analyses have been conducted on planktonic and benthic foraminifera from the western North Atlantic to reconstruct sea surface temperatures (SSTs) and deep water temperatures and the structure of the water column around this major biotic turnover. Whilst the extinctions of M. spinulosa and A. praetopilensis occur during a long-term cooling trend, the biotic turnover in the muricate group does not appear to be related to significant climatic change. Sea surface temperatures decrease slowly prior to the extinction events, and there is no evidence for a large-temperature shift associated with the faunal changes. The turnover event was therefore probably related to the increased surface water productivity and the deterioration of photosymbiotic partnerships with algae.

Isotope measurements from late Paleocene - early Eocene of 5 cores from Atlantic and Pacific Ocean

High-resolution stable carbon isotope records for upper Paleocene - lower Eocene sections at Ocean Drilling Program Sites 1051 and 690 and Deep Sea Drilling Project Sites 550 and 577 show numerous rapid (40 - 60 kyr duration) negative excursions of up to 1 per mill. We demonstrate that these transient decreases are the expected result of nonlinear insolation forcing of the carbon cycle in the context of a long carbon residence time. The transients occur at maxima in Earth's orbital eccentricity, which result in high-amplitude variations in insolation due to forcing by climatic precession. The construction of accurate orbital chronologies for geologic sections older than ~ 35 Ma relies on identifying a high-fidelity recorder of variations in Earth's orbital eccentricity. We use the carbon isotope records as such a recorder, establishing a robust orbitally tuned chronology for latest Paleocene-earliest Eocene events. Moreover, the transient decreases provide a means of precise correlation among the four sites that is independent of magnetostratigraphic and biostratigraphic data at the <10^5-year scale. While the eccentricity-controlled transient decreases bear some resemblance to the much larger-amplitude carbon isotope excursion (CIE) that marks the Paleocene/Eocene boundary, the latter event is found to occur near a minimum in the ~400-kyr eccentricity cycle. Thus the CIE occurred during a time of minimal variability in insolation, the dominant mechanism for forcing climate change on 104-year scales. We argue that this is inconsistent with mechanisms that rely on a threshold climate event to trigger the Paleocene/Eocene thermal maximum since any threshold would more likely be crossed during a period of high-amplitude climate variations.