Subsurface Dwelling Research Articles

Leeuwin current dynamics in the SE Indian Ocean and implications for regional surface hydrography since the latest Miocene: Results from ODP Site 763A

This study examines the relationship between the ocean circulation dynamics in the eastern Indian Ocean and climate variability in Northwest (NW) Australia over the last 6.1 million years. The vertical water column of the southeastern Indian Ocean was analyzed using planktic foraminifera assemblages, and oxygen and carbon isotope ratios of surface and subsurface dwelling foraminifera from Ocean Drilling Program (ODP) Site 763A. The X-ray fluorescence data of bulk sediment from ODP Site 763A was also used to understand variability in relative humidity and aridity in NW Australia associated with surface ocean warming. The findings suggest a pronounced change in surface oceanography and climate in the region from 5.4 to 5 Ma, indicating a weak Leeuwin Current (LC) and reduction in mixed layer thickness. Subsequently, between 5.0 and 3.6 Ma, a strongly stratified water column with a thick mixed layer and deep thermocline emerged owing to the intensified Indonesian Throughflow (ITF). This led to a strengthened LC and diminished surface productivity, corresponding to a wet phase in NW Australia. The closure of the Indonesian Seaway during the Middle Pliocene (3.6–3.2 Ma) restricted the flow of West Pacific Warm Water into the Indian Ocean, weakened the LC and intensified the dry phase in NW Australia. Significant shifts in planktic foraminifera abundances are observed in the early Pleistocene (2.6–1.2 Ma) perhaps linked to major changes in surface ocean circulation. During the Mid-Pleistocene Transition (1.2–0.6 Ma), the West Australian Current exerted a significant influence over Site 763A.

Estimates of Pliocene Tropical Pacific Temperature Sensitivity to Radiative Greenhouse Gas Forcing

AbstractThe Western Equatorial Pacific (WEP) warm pool, with surface temperatures >28 °C and a deep thermocline, is an important source of latent and sensible heat for the global climate system. Because the tropics are not sensitive to ice‐albedo feedbacks, the WEP's response to radiative forcing can be used to constrain a minimum estimate of Earth system sensitivity. Climate modeling of pCO2‐radiative warming projections shows little change in WEP variability; here we use temperature distributions of individual surface and subsurface dwelling fossil foraminifera to evaluate past variability and possible radiative and dynamic climate forcing over the Plio‐Pleistocene. We investigate WEP warm pool variability within paired glacial‐interglacial (G‐IG) intervals for four times: the Holocene‐Last Glacial Maximum, ~2, ~3, and ~4 Ma. Our results show that these surface and subsurface temperature distributions are similar for all G‐IG pairs, indicating no change in variability, even as pCO2‐radiative forcing and other boundary conditions changed on G‐IG timescales. Plio‐Pleistocene sea surface temperature (SST) distributions are similar to those from the Holocene, indicating WEP SSTs respond to pCO2‐radiative forcing and associated feedbacks. In contrast, Plio‐Pleistocene subsurface temperature distributions suggest subsurface temperatures respond to changes in thermocline temperature and depth. We estimate tropical temperature sensitivity for the mid‐Pliocene (~3 Ma) using our individual foraminifera SST data set and a previously published high‐resolution boron isotope‐based pCO2 reconstruction. We find tropical temperature sensitivity was equal to, or less than, that of the Late Pleistocene.

The calcification depth and Mg/Ca thermometry of Pulleniatina obliquiloculata in the tropical Indo-Pacific: A core-top study

Abstract A sub-surface dwelling planktonic foraminifer, Pulleniatina obliquiloculata, in particular its shell's geochemical properties such as stable oxygen isotopic composition and Mg/Ca ratios, are widely used to reconstruct past changes in the thermocline of tropical Indo-Pacific. However, the depth range that P. obliquiloculata population generally dwells or calcifies has been shown to significantly vary, depending on the regions and the seasons. In this study, δ18O and Mg/Ca of core-top P. obliquiloculata from the tropical Indo-Pacific are analyzed by means of comparison with modern hydrographic data. We apply a δ18O-based approach to decipher the varying apparent calcification depth (ACD) of this species for the tropical Indo-Pacific, and find that P. obliquiloculata's ACD varies between 50 and 150 m regionally, in connection with local oceanographic settings. At given ACD, exponential relationships between temperature and P. obliquiloculata Mg/Ca are determined as Mg/Ca = 0.245 ± 0.041 exp. (0.088 ± 0.009 T) for these core-top samples. The sensitivity of P. obliquiloculata Mg/Ca to temperature is in good accordance with most previous findings, particularly the recent work using core-top samples from the western tropical Pacific. Taken together, our results not only improve the understanding of the calcification conditions of P. obliquiloculata, but also make it possible to better estimate the sub-surface temperature of the Indo-Pacific Warm Pool (IPWP) using Late-Quaternary sedimentary materials.

A Deep Eastern Equatorial Pacific Thermocline During the Last Glacial Maximum

AbstractThe mean state and variability of the tropical Pacific is influenced by the depth of the thermocline. During the Last Glacial Maximum (~21,000 years ago), the zonal sea surface temperature gradient across the equatorial Pacific was reduced and productivity was generally lower than modern. To understand the thermocline depth's role in determining the Last Glacial Maximum tropical mean state, we reconstruct the upper ocean δ18O profile from multiple species of planktic foraminifera. We synthesize existing records of surface and subsurface dwelling foraminifera to reconstruct the vertical δ18O gradient throughout the eastern equatorial Pacific. We find the thermocline was deeper during the Last Glacial Maximum than the Holocene throughout the eastern equatorial Pacific region. The thermocline depth's role in the dynamic forcing of the cold tongue contributed to the reduced zonal SST gradient across the equatorial Pacific, decreased productivity, and presumably impacted El Niño‐Southern Oscillation variability relative to the Holocene.

Holocene evolution of the North Atlantic subsurface transport

Abstract. Previous studies suggested that short-term freshening events in the subpolar gyre can be counterbalanced by advection of saline waters from the subtropical gyre and thus stabilize the Atlantic Meridional Overturning Circulation (AMOC). However, little is known about the inter-gyre transport pathways. Here, we infer changes in surface and subsurface transport between the subtropical and polar North Atlantic during the last 11 000 years, by combining new temperature and salinity reconstructions obtained from combined δ18O and Mg ∕ Ca measurements on surface and subsurface dwelling foraminifera with published foraminiferal abundance data from the subtropical North Atlantic, and with salinity and temperature data from the tropical and subpolar North Atlantic. This compilation implies an overall stable subtropical warm surface water transport since 10 ka BP. In contrast, subsurface warm water transport started at about 8 ka but still with subsurface heat storage in the subtropical gyre. The full strength of intergyre exchange was probably reached only after the onset of northward transport of warm saline subsurface waters at about 7 ka BP, associated with the onset of the modern AMOC mode. A critical evaluation of different potential forcing mechanisms leads to the assumption that freshwater supply from the Laurentide Ice Sheet was the main control on subtropical to subpolar ocean transport at surface and subsurface levels.

The Impact of the Latest Danian Event on Planktic Foraminiferal Faunas at ODP Site 1210 (Shatsky Rise, Pacific Ocean).

The marine ecosystem has been severely disturbed by several transient paleoenvironmental events (<200 kyr duration) during the early Paleogene, of which the Paleocene-Eocene Thermal Maximum (PETM, ~56 Ma) was the most prominent. Over the last decade a number of similar events of Paleocene and Eocene age have been discovered. However, relatively little attention has been paid to pre-PETM events, such as the “Latest Danian Event” ("LDE", ~62.18 Ma), specifically from an open ocean perspective. Here we present new foraminiferal isotope (δ13C, δ18O) and faunal data from Ocean Drilling Program (ODP) Site 1210 at Shatsky Rise (Pacific Ocean) in order to reconstruct the prevailing paleoceanographic conditions. The studied five-meter-thick succession covers ~900 kyr and includes the 200-kyr-lasting LDE. All groups surface dwelling, subsurface dwelling and benthic foraminifera show a negative δ13C excursion of >0.6‰, similar in magnitude to the one previously reported from neighboring Site 1209 for benthic foraminifera. δ18O-inferred warming by 1.6 to 2.8°C (0.4–0.7‰ δ18O measured on benthic and planktic foraminiferal tests) of the entire water column accompanies the negative δ13C excursion. A well stratified upper ocean directly before and during the LDE is proposed based on the stable isotope gradients between surface and subsurface dwellers. The gradient is less well developed, but still enhanced after the event. Isotope data are supplemented by comprehensive planktic foraminiferal faunal analyses revealing a dominance of Morozovella species together with Parasubbotina species. Subsurface-dwelling Parasubbotina shows high abundances during the LDE tracing changes in the strength of the isotope gradients and, thus, may indicate optimal living conditions within a well stratified surface ocean for this taxon. In addition, distinct faunal changes are reported like the disappearance of Praemurica species right at the base of the LDE and the continuous replacement of M. praeangulata with M. angulata across the LDE.

Response of the subtropical North Atlantic surface hydrography on deglacial and Holocene AMOC changes

AbstractThe North Atlantic subtropical gyre (STG) circulates warm waters between 10 and 40°N and is a potential area of heat storage during periods of reduced North Atlantic Meridional Overturning Circulation (AMOC), when warm salt‐rich waters are retained in the subtropics. In this study, we investigated multicentennial to millennial scale changes in subtropical North Atlantic hydrography in response to AMOC changes during the last deglaciation and early Holocene, using sediment cores MD08‐3180 and GEOFAR KF16. The coring site (38°N) is situated near the boundary between transitional eastern North Atlantic waters and STG waters that is formed by the Azores Front. Hydrographic changes are reconstructed using new stable isotope data of benthic and subsurface dwelling planktonic foraminifera, Mg/Ca measurements on planktonic foraminifera, and planktonic foraminifera abundances that are supplemented with published sea surface temperature and stable isotope data. These multiproxy data indicate a close coupling between the latitudinal position of the northern STG boundary and deglacial AMOC modes. During weak AMOC phases (Heinrich event 1, Younger Dryas (YD), 8.2 ka event), Northern Hemisphere subpolar water reached down to the northern STG boundary, displacing the boundary southward. During the Bølling‐Allerød warm period, a strong warming trend of the subtropical region to 19°C is observed. A cooling of the sea surface temperature by 6°C during the YD is accompanied by ongoing northward transport of warm subsurface water that might have contributed to the restart of AMOC.

Deglacial ocean warming and marine margin retreat of the Cordilleran Ice Sheet in the North Pacific Ocean

A new, high-resolution planktonic foraminiferal Mg/Ca-based ocean temperature record has been generated for deep sea core MD02-2496, sited offshore of Vancouver Island, Western Canada during the last deglaciation (21–12 ka). The relationship between Cordilleran Ice Sheet (CIS) retreat and changing regional ocean temperatures has been reconstructed through glaciomarine sediments in MD02-2496 that capture tidewater glacier response to surface ocean thermal forcing. At CIS maximum extent, the marine margin of the ice sheet advanced onto the continental shelf. During this interval, ocean temperatures recorded by surface dwelling Globigerina bulloides remained a relatively constant ∼7.5 °C while subsurface dwelling Neogloboquadrina pachyderma (s.) recorded temperatures of ∼5 °C. These ocean temperatures were sufficiently warm to induce significant melt along the tidewater ice terminus similar to modern Alaskan tidewater glacial systems. During the deglacial retreat of the CIS, the N. pachyderma temperature record shows two distinct warming steps of ∼2 and 2.5°C between 17.2–16 and 15.5–14 ka respectively, coincident with ice rafting events from the CIS, while G. bulloides records an ∼3°C warming from 15 to 14 ka. We hypothesize that submarine melting resulting from relatively warm ocean temperatures was an important process driving ice removal from CIS tidewater glaciers during the initial stages of deglaciation.

Trace element variability in crust-bearing and non crust-bearing Neogloboquadrina incompta, P–D intergrade and Globoconella inflata from the Southwest Pacific Ocean: Potential paleoceanographic implications

Mg/Ca and Sr/Ca ratios were measured in the sub-surface dwelling planktonic foraminifera Neogloboquadrina incompta, Neogloboquadrina pachyderma–Neogloboquadrina dutertrei (P–D) intergrades and Globoconella inflata from core–top, dredge and plankton tow material from the Southwest Pacific Ocean. The presence of outer crusts on each foraminifera test was determined using a scanning electron microscope, after trace element analysis using laser ablation inductively coupled plasma mass spectrometry (LA–ICPMS). Our laser ablation profiles allow an arbitrary distinction between crust and inner calcite Mg/Ca values, with the former exhibiting consistently lower Mg/Ca by up to 56% depending on both the species and core–top location analyzed. The lower crust Mg/Ca values suggest that 1) crust formation may be initiated at a specific (low) temperature or, 2) crust-calcite no longer follows the Mg to Ca thermodynamic relationship typically associated with foraminiferal primary calcite. For Sr/Ca ratios, we did not observe any difference between crust in and inner calcite. The thickness of the crust between measured individual chambers varied, such that whole test Mg/Ca were affected by variable crustal thickness across all chambers. This study shows that increasing ratios of crust to non crust-bearing tests in N. incompta, P–D intergrades and G. inflata have the potential to lower the bulk composition of Mg/Ca, thus resulting in biased cooler temperature reconstructions.

Glacial Southern Ocean freshening at the onset of the Middle Pleistocene Climate Transition

Changes in Southern Ocean hydrography may have played an important role in the Middle Pleistocene Transition (MPT), particularly through their impact on ocean circulation and atmospheric CO2 concentrations. Here we present foraminiferal Mg/Ca and δ18O results for the subsurface dwelling planktonic foraminifer Neogloboquadrina pachyderma (sinistral) at the Ocean Drilling Program (ODP) Site 1090. Results are used to reconstruct upper ocean temperatures and derive seawater δ18O in the Subantarctic Atlantic Ocean during the MPT. The new records indicate that, starting at ∼1250ka, glacial temperatures and local (ice volume corrected) seawater δ18O in the upper water column of the Subantarctic Atlantic Ocean decreased, pointing to cooler (∼2°C) and fresher (∼0.4‰) conditions than in the preceding glacial stages. These upper ocean hydrographic changes broadly coincide with the increase in the power of the 100ky glacial–interglacial cycle in both records and with a shift towards decreased deep ventilation in the glacial Southern Ocean. Our finding suggests that an increase in Southern Ocean stratification, driven by the observed freshening of the upper water column, may have reduced the exchange of carbon between the deep Southern Ocean and the atmosphere during glacial stages. This process may have contributed, in combination with other mechanisms, to lower glacial atmospheric CO2 concentrations during the MPT.

Mg/Ca ratios of single planktonic foraminifer shells and the potential to reconstruct the thermal seasonality of the water column

Mg/Ca ratios of surface and subsurface dwelling foraminifera provide valuable information about the past temperature of the water column. Planktonic foraminifera calcify over a period of weeks to months. Therefore, the range of Mg/Ca temperatures obtained from single specimens potentially records seasonal temperature changes. We present solution‐derived Mg/Ca ratios for single specimens of the planktonic foraminifera species Globigerinoides ruber (pink), Globigerinoides ruber (white), and Globorotalia inflata from a sediment trap off northwest Africa (20°45.6′N, 18°41.9′W). Cleaning of single specimens was achieved using a flow‐through system in order to prevent sample loss. Mg/Ca ratios of surface dwelling G. ruber (pink) show strong seasonality linked to sea surface temperature. Mg/Ca ratios of G. ruber (white) do not show such seasonality. Subsurface dwelling G. inflata flux is largest during the main upwelling season, but Mg/Ca ratios reflect annual temperatures at intermediate water depths. The sediment trap time series suggests that changes in the range of Mg/Ca ratios exhibited by single specimens of G. ruber (pink) and G. inflata from the sedimentary record should provide information on the past temperature range under which these species calcified. Statistical analysis suggests detectable changes in the Mg/Ca range are ≥0.80 mmol/mol (G. ruber (pink)) and ≥0.34 mmol/mol (G. inflata). For G. ruber (pink), such changes would indicate changes in the seasonal sea surface temperature range &gt;4°C or a shift in the main calcification and reproductive period. For G. inflata, such changes would indicate &gt;1.7°C changes in the thermocline temperature or a change in the depth habitat.

COMPLEX TETRAPOD BURROWS FROM MIDDLE TRIASSIC RED BEDS OF THE ARGANA BASIN (WESTERN HIGH ATLAS, MOROCCO)

Although burrowing ability has been widespread in tetrapods for more than 300 million years, subsurface dwelling structures that indicate communal behavior are poorly evidenced from pre-Cenozoic strata. Here we present recently discovered tetrapod burrows from Middle Triassic red beds of the Argana Basin in central Morocco, whose complexity suggests an origin by gregarious animals. The well-preserved burrows occur in interbedded mudstones and sandstones interpreted as channel and overbank deposits of ephemeral, braided streams. All burrows originate from the top of thick-bedded sandstones and descend as moderately inclined (10°–30°), partially spiral tunnels to laterally extended, branched chambers in underlying mudstones. Tunnel segments are biconvex to planoconvex in cross section, up to 20 cm wide and 12 cm in maximum height and exhibit transverse scratch marks along the ceilings and sidewalls. Distinctive burrow characteristics include a laterally sinuous geometry (wavelength λ = 38–45 cm; amplitude A = 5–10 cm) of the tubelike passages and the presence of grouped alcoves in terminal chambers. We attribute the burrows to procolophonids or therapsids based on closely associated tetrapod tracks and the limited diameter of the excavations. Our findings represent the second oldest record of communal fossorial behavior by tetrapods and the oldest example from low-latitude areas. Beyond providing refuge from predators, these elaborate underground structures probably functioned as a buffer against diurnal or seasonal variations of air temperature and humidity in a semiarid habitat that was situated just north of the paleoequator.

In situ bacterial colonization of compacted bentonite under deep geological high-level radioactive waste repository conditions

Subsurface microorganisms are expected to invade, colonize, and influence the safety performance of deep geological spent nuclear fuel (SNF) repositories. An understanding of the interactions of subsurface dwelling microbial communities with the storage is thus essential. For this to be achieved, experiments must be conducted under in situ conditions. We investigated the presence of groundwater microorganisms in repository bentonite saturated with groundwater recovered from tests conducted at the Aspö underground Hard Rock Laboratory in Sweden. A 16S ribosomal RNA and dissimilatory bisulfite reductase gene distribution between the bentonite and groundwater samples suggested that the sulfate-reducing bacteria widespread in the aquifers were not common in the clay. Aerophilic bacteria could be cultured from samples run at <or=55 degrees C but not at >or=67 degrees C. Generally, the largely gram-negative groundwater microorganisms were poorly represented in the bentonite while the gram-positive bacteria commonly found in the clay predominated. Thus, bentonite compacted to a density of approximately 2 g cm(-3) together with elevated temperatures might discourage the mass introduction of the predominantly mesophilic granitic aquifer bacteria into future SNF repositories in the long run.

Quaternary upper ocean thermal gradient variations in the South China Sea: Implications for east Asian monsoon climate

The east Asian monsoon climate has an overwhelming influence on local climatic conditions of the South China Sea (SCS). Here we present results from a 3‐year study of modern sediment traps from the central SCS in which the percentage of opal, the fluxes of Pulleniatina obliquiloculata and Globigerinoides ruber, the organic carbon flux, and primary productivity all show highest values during winter when the mixed layer depth is deepest. The δ18O difference (Δδ18O(P‐G)) between the subsurface dwelling P. obliquiloculata and the mixed layer dwelling G. ruber in core top samples from 12 piston cores and one Ocean Drilling Program (ODP) site in the SCS is large, ∼0.6‰ in a cold eddy area with a shallow mixed layer off Vietnam, but is reduced in deep mixed layer settings lacking cold eddies. We also present 1.56 Myr‐long isotope records of G. ruber and P. obliquiloculata from ODP site 1143 in the southern SCS that reveal upper ocean thermal gradient variations during the Quaternary. Lower Δδ18O(P‐G) values indicate increased mixed layer depths over most glacial episodes, likely due to stronger winter monsoon winds. In contrast, higher Δδ18O(P‐G) values during interglacial intervals suggest decreased mixed layer depths and thus weaker winter monsoon winds. Comparisons of Δδ18O(P‐G) with the percentage of P. obliquiloculata at site 1143 and the percentage of herbs and opal flux at site 1144 demonstrate that glacial‐interglacial variations were strongly influenced by stronger and weaker east Asian winter monsoons during glacials and interglacials, respectively. Therefore the upper ocean thermal gradient variations in the SCS have been consistently affected by the east Asian winter monsoon since at least the beginning of the Pleistocene.

Subsurface Dwelling Crustaceans as Indicators of Hydrological Conditions, Oxygen Concentrations, and Sediment Structure in an Alluvial Aquifer

AbstractThe relation between environmental conditions and the species composition and individual abundance of crustaceans was investigated in a shallow alluvial aquifer, located in the Danube wetlands (Lobau, Austria). Samples, consisting of groundwater, sediment, and fauna, were taken from permanent installed wells by means of a piston pump five times in a year cycle.The results show that the spatial and temporal distribution, individual abundance, and species richness of crustacean fauna is related to hydrological conditions, oxygen concentrations, and geologic structures in the alluvial aquifer. Therefore, crustaceans, divided in stygoxene, stygophile, and stygobite species, can be used as bioindicators of these environmental conditions in an aquifer. It is suggested that beside physicochemical analyses also the crustacean fauna should be considered to characterise a groundwater ecosystem.

Needed: A New Cadre of Applied Scientists Skilled in Basic Science, Communication, and Aquatic Resource Management

Previous articleNext article No AccessBridgesNeeded: A New Cadre of Applied Scientists Skilled in Basic Science, Communication, and Aquatic Resource ManagementNicholas G. Aumen and Karl E. HavensNicholas G. Aumen Search for more articles by this author and Karl E. Havens Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by Volume 16, Number 3Sep., 1997 Article DOIhttps://doi.org/10.2307/1468155 Views: 5Total views on this site Citations: 9Citations are reported from Crossref Journal History This article was published in the Journal of the North American Benthological Society (1986-2011), which is continued by Freshwater Science (2012-present). Copyright 1997 The North American Benthological SocietyPDF download Crossref reports the following articles citing this article:David Kraff, Alan D. Steinman Integrated watershed management in Michigan: Challenges and proposed solutions, Journal of Great Lakes Research 44, no.11 (Feb 2018): 197–207.https://doi.org/10.1016/j.jglr.2017.10.007K.L. Laurent, K.B. Friedman, G. Krantzberg, D. Scavia, I.F. Creed Scenario analysis: An integrative and effective method for bridging disciplines and achieving a thriving Great Lakes-St. Lawrence River basin, Journal of Great Lakes Research 41 (Jan 2015): 12–19.https://doi.org/10.1016/j.jglr.2014.10.002R. Jan Stevenson, Sergi Sabater Understanding effects of global change on river ecosystems: science to support policy in a changing world, Hydrobiologia 657, no.11 (Aug 2010): 3–18.https://doi.org/10.1007/s10750-010-0392-7Nicholas G. Aumen,5 Martin E. Gurtz,6 Michael T. Barbour,7 and Ashley Moerke8 BRIDGES: evolution of basic and applied linkages in benthic science, Journal of the North American Benthological Society 29, no.11 (Jul 2015): 359–371.https://doi.org/10.1899/08-031.1R. Jan Stevenson, Sergi Sabater Understanding effects of global change on river ecosystems: science to support policy in a changing world, (Jan 2010): 3–18.https://doi.org/10.1007/978-94-007-0608-8_2SARA E. JOHNSON, BRIAN E. GRABER Enlisting the Social Sciences in Decisions about Dam Removal, BioScience 52, no.88 (Jan 2002): 731.https://doi.org/10.1641/0006-3568(2002)052[0731:ETSSID]2.0.CO;2RONALD BJORKLAND, CATHERINE M. PRINGLE Educating Our Communities and Ourselves about Conservation of Aquatic Resources through Environmental Outreach, BioScience 51, no.44 (Jan 2001): 279.https://doi.org/10.1641/0006-3568(2001)051[0279:EOCAOA]2.0.CO;2Garth W. Redfield ECOLOGICAL RESEARCH FOR AQUATIC SCIENCE AND ENVIRONMENTAL RESTORATION IN SOUTH FLORIDA, Ecological Applications 10, no.44 (Aug 2000): 990–1005.https://doi.org/10.1890/1051-0761(2000)010[0990:ERFASA]2.0.CO;2Friederike Mösslacher Subsurface Dwelling Crustaceans as Indicators of Hydrological Conditions, Oxygen Concentrations, and Sediment Structure in an Alluvial Aquifer, International Review of Hydrobiology 83, no.44 (Jan 1998): 349–364.https://doi.org/10.1002/iroh.19980830410

Benthic response to a pelagic front

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 147:49-62 (1997) - doi:10.3354/meps147049 Benthic response to a pelagic front Josefson AB, Conley DJ With the aim of studying the influence of pelagic front primary production on the benthic system underneath, biomarkers of benthic organic matter constituents and macrofaunal abundance and biomass were measured on stations in a grid extending through the area of the Skagerrak-Kattegat pelagic plume front. A time persistent pattern of chl a and phaeopigments in the surface sediment was observed, with chl a / chl a + phaeopigments ratios exceeding 0.5, suggesting high input of phytoplankton to the bottom near the front. Of the sediment variables chl a, phaeopigments, particulate organic nitrogen (PON), particulate organic carbon (POC) and biogenic silica (BSi), the pigments showed the highest correlation with benthic biomass and abundance. Chl a and phaeopigments together explained nearly half of the variation in benthic biomass and the non-polychaete fraction of abundance. C/N ratio showed the expected negative relationship with biomass but was not statistically significant. PON, BSi and POC were poor indicators of faunal variables. Results suggest that sediment chlorophyll and its breakdown products may be useful biomarkers of labile organic matter. The organic matter (OM) gradient significantly influenced faunal structure. Polychaete and echinoderm AFDW were positively correlated with chl a and with phaeopigments. A major part of the positive faunal response was due to the burrowing ophiuroid Amphiura filiformis and its commensal Mysella bidentata. While the host was best correlated with phaeopigments, the commensal correlated equally well with both chl a and phaeopigments. Faunal changes in composition suggested increased importance of subsurface feeding deep in the sediment in response to increased OM loading. Surface deposit-feeders did not respond to the high levels of labile OM in the middle of the area. Results indicate strong pelagic-benthic coupling near the front and in the area with a mixed water column and are consistent with the hypotheses that pelagic-benthic energy coupling is stronger in mixed areas compared to those which are stratified and that increased OM loading may increase subsurface dwelling and OM processing through benthic burrowing biomass. Pelagic-benthic coupling · Biomass · Fronts · Chlorophyll Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 147. Publication date: February 27, 1997 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1997 Inter-Research.

The carbon isotope distribution in the deep ΣCO 2 and benthic foraminifers of the Alboran Basin, western Mediterranean: Implications for variations in primary production levels since the last deglaciation

High productivity in areas within the Alboran Sea could be responsible for a 0.9‰ 13C depletion of Uvigerina peregrina shells when compared to other western Mediterranean basins. At present however, the δ 13C variations of the total dissolved inorganic carbon of bottom waters do not exceed 0.2‰ within the Alboran basin, reflecting minor re-mineralization of organic matter. Thus, it is suggested that δ 13C values of modern U. peregrina can be linked to those of the pore water ΣCO 2 and that rain of particulate organic matter to the seafloor results in an important 13C gradient at the bottom water-sediment interface of the Alboran basin. Last deglaciation changes in the relative abundances of three species of endobenthic foraminifers, estimated through the following index: Log[( Melonis barleeanum + Globobulimina affinis)/( Uvigerina peregrina + 1)], record depth migrations within the sediments of the O 2 minimum level. These migrations are thought to correlate with surface water productivity changes. Low values of this index before approximately 13 kyr and after 9 kyr would indicate an enhanced flux of organic matter to the seafloor resulting itself from an increased surficial productivity. This is apparently supported by a high production of diatoms valves before 13 kyr, higher percentages of U. peregrina and lower Uvigerina δ 13C values before 13 kyr and after 9 kyr. In the time interval 9-6 kyr however, the absence of diatoms, the stronger Δδ 13C gradient between surface and subsurface dwelling planktonic foraminifers, suggest that recycling of the organic matter was intensified in subsurface waters. This event coincides in time with the deepening of the pycnocline at 9 kyr in the Alboran Sea, which marks the onset of present-day hydrographic conditions. It also coincides with the deposition of sapropel S1 and with the stagnation of the Eastern Mediterranean basin which induced a lower ventilation of Mediterranean Waters at intermediate depths. The relatively low organic carbon contents measured in one of the cores, apparently contradict the proposed scenarios. In fact, higher production levels do not necessarily imply a higher organic carbon content in the underlying sediments. Within well oxygenated bottom waters, the organic carbon preservation is also very sensitive to sedimentation rate as well as to near surface compaction effects on early diagenesis.

Pseudopodia of surface and subsurface dwelling Miliammina fusca (Brady)

Other| July 01, 1975 Pseudopodia of surface and subsurface dwelling Miliammina fusca (Brady) Larry Frankel Larry Frankel Univ. Conn., Storrs, Conn., United States Search for other works by this author on: GSW Google Scholar Journal of Foraminiferal Research (1975) 5 (3): 211–217. https://doi.org/10.2113/gsjfr.5.3.211 Article history first online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Larry Frankel; Pseudopodia of surface and subsurface dwelling Miliammina fusca (Brady). Journal of Foraminiferal Research 1975;; 5 (3): 211–217. doi: https://doi.org/10.2113/gsjfr.5.3.211 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu nav search search input Search input auto suggest search filter All ContentBy SocietyJournal of Foraminiferal Research Search Advanced Search This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.