GLORIA — GEOMAR Library Ocean Research Information Access

1

Online Resource

Late Quaternary Changes in Silicate Utilisation and Upwelling Intensity off Peru : Insights from Silicon and Neodymium Isotopes (2012)

Ehlert, Claudia

add to mindlist on the mindlist

Details Availability

Keywords: Hochschulschrift ; Peru ; Holozän ; Siliciumisotop ; Neodymisotop

Type of Medium: Online Resource

Pages: Online-Ressource

URL: http://nbn-resolving.de/urn:nbn:de:gbv:8-diss-77598

URL: http://d-nb.info/1020283777/34

URL: http://eldiss.uni-kiel.de/macau/receive/dissertation_diss_00007759

URN: urn:nbn:de:gbv:8-diss-77598

DDC: 550

Language: English

Note: Kiel, Univ., Diss., 2012

Permalink

	Location	Call Number	Limitation	Availability

Others were also interested in ...

GEOMAR CATALOGUE

Link to Library Catalog

2

Unknown

Dissolved Si isotope composition measured in water samples during METEOR cruises M77/3 and M77/4 (2013)

Grasse, Patricia ; Ehlert, Claudia ; Frank, Martin

PANGAEA

In: Supplement to: Grasse, Patricia; Ehlert, Claudia; Frank, Martin (2013): The influence of water mass mixing on the dissolved Si isotope composition in the Eastern Equatorial Pacific. Earth and Planetary Science Letters, 380, 60-71, https://doi.org/10.1016/j.epsl.2013.07.033

add to mindlist on the mindlist

Details

Publication Date: 2024-05-22

Description: Silicon isotopes are a powerful tool to investigate the cycling of dissolved silicon (Si). In this study the distribution of the Si isotope composition of dissolved silicic acid (d30Si(OH)4) was analyzed in the water column of the Eastern Equatorial Pacific (EEP) where one of the globally largest Oxygen Minimum Zones (OMZs) is located. Samples were collected at 7 stations along two meridional transects from the equator to 14°S at 85°50'W and 82°00'W off the Ecuadorian and Peruvian coast. Surface waters show a large range in isotope compositions d30Si(OH)4 (+2.2 per mil to +4.4 per mil) with the highest values found at the southernmost station at 14°S. This station also revealed the most depleted silicic acid concentrations (0.2 µmol/kg), which is a function of the high degree of Si utilization by diatoms and admixture with waters from highly productive areas. Samples within the upper water column and the OMZ at oxygen concentrations below 10 µmol/kg are characterized by a large range in d30Si(OH)4, which mainly reflects advection and mixing of different water masses, even though the highly dynamic hydrographic system of the upwelling area off Peru does not allow the identification of clear Si isotope signals for distinct water masses. Therefore we cannot rule out that also dissolution processes have an influence on the d30Si(OH)4 signature in the subsurface water column. Deep water masses (〉2000 m) in the study area show a mean d30Si(OH)4 of +1.2±0.2 per mil, which is in agreement with previous studies from the eastern and central Pacific. Comparison of the new deep water data of this study and previously published data from the central Pacific and Southern Ocean reveal substantially higher d30Si(OH)4 values than deep water signatures from the North Pacific. As there is no clear correlation between d30Si(OH)4 and silicic acid concentrations in the entire data set the distribution of d30Si(OH)4 signatures in deep waters of the Pacific is considered to be mainly a consequence of the mixing of several end member water masses with distinct Si isotope signatures including Lower Circumpolar Deep Water (LCDW) and North Pacific Deep Water (NPDW).

Keywords: Climate - Biogeochemistry Interactions in the Tropical Ocean; CTD/Rosette; CTD-RO; Date/Time of event; Density, sigma-theta (0); DEPTH, water; Elevation of event; Event label; Latitude of event; Longitude of event; M77/3; M77/3-CTD23; M77/3-CTD27; M77/4; M77/4_152; M77/4-CTD18; M77/4-CTD27; M77/4-CTD44; M77/4-CTD64; M77/4-CTD82; Meteor (1986); Nitrate; Oxygen; Phosphate; Salinity; SFB754; Silicate; Temperature, water, potential; δ30Si, silicic acid

Type: Dataset

Format: text/tab-separated-values, 490 data points

Permalink

	Location	Call Number	Limitation	Availability

Others were also interested in ...

DATA PANGAEA

Fulltext

3

Unknown

Silicon isotope constraints on sources and utilization of silicic acid in the northern South China Sea (2012)

Cao, Zhimian ; Frank, Martin ; Dai, Minhan ; [et al.]

Elsevier

In: Geochimica et Cosmochimica Acta, 97 . pp. 88-104.

add to mindlist on the mindlist

Details

Publication Date: 2019-09-23

Description: The stable silicon isotopic composition (δ30Si) of waters and diatoms has increasingly been used to investigate the biogeochemical cycling of Si in the major ocean basins. Here we present the first Si isotope data set from the northern South China Sea (NSCS), a large marginal sea system in the western North Pacific to examine sources and utilization of silicic acid (Si(OH)4). During two cruises in July–August 2009 (summer) and January 2010 (winter), samples for isotope measurements of dissolved Si(OH)4 (δ30SiSi(OH)4) and of biogenic silica (δ30SiBSi) in suspended particles were collected along a transect perpendicular to the coast from the inner shelf to the deep-water slope, as well as at the South East Asian Time-series Study (SEATS) station located in the NSCS basin. Surface δ30SiSi(OH)4 generally increased from values ∼+2.3‰ on the inner shelf to ∼+2.8‰ above the deep basin, suggesting an increasing utilization of dissolved Si(OH)4 reflecting the transition from eutrophic to oligotrophic conditions. The δ30SiBSi values were systematically lower than the corresponding δ30SiSi(OH)4 in the euphotic zone (above 100 m) on the shelf and slope. In contrast at station SEATS in the NSCS basin, δ30SiBSi signatures in both seasons were within error equal to δ30SiSi(OH)4 in the surface mixed layer (above 50 m) and δ30SiBSi in waters below were significantly higher than the corresponding δ30SiSi(OH)4. By comparing the field data with the Si isotope fractionation revealed by the Rayleigh or the steady state models, we demonstrate the existence of variable Si(OH)4 origins in different areas of the NSCS. Surface waters on the inner shelf were largely fed by nutrients from the Pearl River input. While the primary source of Si(OH)4 for the euphotic zone on the outer shelf and slope was upwelling or vertical mixing from underlying waters, the Si(OH)4 in the surface mixed layer of the NSCS basin might have originated from horizontal mixing with other highly fractionated surface waters. As a consequence, the Si isotope dynamics in the NSCS are largely controlled by variable biological fractionation of Si in waters from different sources with different initial Si isotopic compositions rather than any single source water.

Type: Article , PeerReviewed

Format: text

DOI: 10.1016/j.gca.2012.08.039

Permalink

	Location	Call Number	Limitation	Availability

Others were also interested in ...

OceanRep: Article in a Scientific Journal - peer-reviewed

PDF

Fulltext

4

Unknown

Contribution of changes in opal productivity and nutrient distribution in the coastal upwelling systems to Late Pliocene/Early Pleistocene climate cooling (2012)

Etourneau, Johan ; Ehlert, Claudia ; Frank, Martin ; [et al.]

Copernicus Publications (EGU)

In: Climate of the Past, 8 (5). pp. 1435-1445.

add to mindlist on the mindlist

Details

Publication Date: 2019-09-23

Description: The global Late Pliocene/Early Pleistocene cooling (~3.0–2.0 million years ago – Ma) concurred with extremely high diatom and biogenic opal production in most of the major coastal upwelling regions. This phenomenon was particularly pronounced in the Benguela upwelling system (BUS), off Namibia, where it is known as the Matuyama Diatom Maximum (MDM). Our study focuses on a new diatom silicon isotope (δ30Si) record covering the MDM in the BUS. Unexpectedly, the variations in δ30Si signal follow biogenic opal content, whereby the highest δ30Si values correspond to the highest biogenic opal content. We interpret the higher δ30Si values during the MDM as a result of a stronger degree of silicate utilisation in the surface waters caused by high productivity of mat-forming diatom species. This was most likely promoted by weak upwelling intensity dominating the BUS during the Late Pliocene/Early Pleistocene cooling combined with a large silicate supply derived from a strong Southern Ocean nutrient leakage responding to the expansion of Antarctic ice cover and the resulting stratification of the polar ocean 3.0–2.7 Ma ago. A similar scenario is hypothesized for other major coastal upwelling systems (e.g. off California) during this time interval, suggesting that the efficiency of the biological carbon pump was probably sufficiently enhanced in these regions during the MDM to have significantly increased the transport of atmospheric CO2 to the deep ocean. In addition, the coeval extension of the area of surface water stratification in both the Southern Ocean and the North Pacific, which decreased CO2 release to the atmosphere, led to further enhanced atmospheric CO2 drawn-down and thus contributed significantly to Late Pliocene/Early Pleistocene cooling.

Type: Article , PeerReviewed

Format: text

DOI: 10.5194/cp-8-1435-2012

Permalink

	Location	Call Number	Limitation	Availability

Others were also interested in ...

OceanRep: Article in a Scientific Journal - peer-reviewed

PDF

Fulltext

5

Unknown

Changes in silicate utilisation and upwelling intensity off Peru since the Last Glacial Maximum – insights from silicon and neodymium isotopes (2013)

Ehlert, Claudia ; Grasse, Patricia ; Frank, Martin

Elsevier

In: Quaternary Science Reviews, 72 . pp. 18-35.

add to mindlist on the mindlist

Details

Publication Date: 2019-09-23

Description: We combine the stable silicon isotope composition (δ30Si) of diatoms and the radiogenic neodymium isotope compositions (εNd) of past seawater extracted from the authigenic fraction of the sediments (Mn–Fe coatings of particles and benthic foraminifers), as well as the radiogenic isotope compositions (Nd, Sr) of the detrital material itself to reconstruct silicic acid utilisation, water mass mixing, and upwelling intensity from the same marine sediments in the Peruvian upwelling region during the past 20,000 years. Additionally, the sedimentary signals were compared to the water column isotope compositions. Along the Peruvian shelf, the dissolved εNd in the water column ranges from −5.7 to +0.6. The corresponding εNd signatures of the coatings and the benthic foraminifers of the surface sediments range from −4.5 to +1.8 and from −2.5 to +2.2, respectively. The detrital εNd (87Sr/86Sr) signatures range from −6.3 to 0 (0.70508–0.71049). All phases show a trend from more radiogenic εNd values in the north towards less radiogenic values in the south broadly reflecting local weathering inputs and hinterland geology. The εNd signatures of the coatings extracted from sediment core SO147-106KL located in the present day centre of coastal upwelling near 12°S have been essentially constant (−1.5) throughout the past 20,000 years, while the detrital εNd (87Sr/86Sr) varied between values of −0.7 (0.70620) during the Last Glacial and −4.5 (0.70849) during the late Holocene reflecting changes in the origin of the sediment and current transport from a more northerly towards a more southerly source and from overall stronger to weaker upwelling. The δ30Si signature of both total biogenic opal (δ30Siopal) and of hand-picked diatoms (δ30Sidiatom) ranged from +0.3‰ (Last Glacial) to +1.4‰ (late Holocene) confirming large variations in upwelling intensity driving silicic acid utilisation by diatoms. Our combined bSiO2 MAR, δ30Siopal and detrital radiogenic isotope results demonstrate that the strongest El Niño-Southern Oscillation conditions off Peru of the past 20 ka have prevailed during the past 5 ka.

Type: Article , PeerReviewed

Format: text

DOI: 10.1016/j.quascirev.2013.04.013

Permalink

	Location	Call Number	Limitation	Availability

Others were also interested in ...

OceanRep: Article in a Scientific Journal - peer-reviewed

PDF

Fulltext

6

Unknown

The influence of water mass mixing on the dissolved Si isotope composition in the Eastern Equatorial Pacific (2013)

Grasse, Patricia ; Ehlert, Claudia ; Frank, Martin

Elsevier

In: Earth and Planetary Science Letters, 380 . pp. 60-71.

add to mindlist on the mindlist

Details

Publication Date: 2019-09-23

Description: Silicon isotopes are a powerful tool to investigate the cycling of dissolved silicon (Si). In this study the distribution of the Si isotope composition of dissolved silicic acid (δ30Si(OH)4) was analyzed in the water column of the Eastern Equatorial Pacific (EEP) where one of the globally largest Oxygen Minimum Zones (OMZs) is located. Samples were collected at 7 stations along two meridional transects from the equator to 14°S at 85°50′W and 82°00′W off the Ecuadorian and Peruvian coast. Surface waters show a large range in isotope compositions δ30Si(OH)4 (+2.2‰ to +4.4‰) with the highest values found at the southernmost station at 14°S. This station also revealed the most depleted silicic acid concentrations (0.2 μmol/kg), which is a function of the high degree of Si utilization by diatoms and admixture with waters from highly productive areas. Samples within the upper water column and the OMZ at oxygen concentrations below 10 μmol/kg are characterized by a large range in δ30Si(OH)4, which mainly reflects advection and mixing of different water masses, even though the highly dynamic hydrographic system of the upwelling area off Peru does not allow the identification of clear Si isotope signals for distinct water masses. Therefore we cannot rule out that also dissolution processes have an influence on the δ30Si(OH)4 signature in the subsurface water column. Deep water masses (〉2000 m) in the study area show a mean δ30Si(OH)4 of +1.2±0.2‰, which is in agreement with previous studies from the eastern and central Pacific. Comparison of the new deep water data of this study and previously published data from the central Pacific and Southern Ocean reveal substantially higher δ30Si(OH)4 values than deep water signatures from the North Pacific. As there is no clear correlation between δ30Si(OH)4 and silicic acid concentrations in the entire data set the distribution of δ30Si(OH)4 signatures in deep waters of the Pacific is considered to be mainly a consequence of the mixing of several end member water masses with distinct Si isotope signatures including Lower Circumpolar Deep Water (LCDW) and North Pacific Deep Water (NPDW).

Type: Article , PeerReviewed

Format: text

DOI: 10.1016/j.epsl.2013.07.033

Permalink

	Location	Call Number	Limitation	Availability

Others were also interested in ...

OceanRep: Article in a Scientific Journal - peer-reviewed

PDF

Fulltext

7

Unknown

Current transport versus continental inputs in the eastern Indian Ocean: Radiogenic isotope signatures of clay size sediments (2011)

Ehlert, Claudia ; Frank, Martin ; Haley, B. A. ; [et al.]

AGU (American Geophysical Union)

In: Geochemistry, Geophysics, Geosystems, 12 (6). Q06017.

add to mindlist on the mindlist

Details

Publication Date: 2018-03-13

Description: Analyses of radiogenic neodymium (Nd), strontium (Sr), and lead (Pb) isotope compositions of clay-sized detrital sediments allow detailed tracing of source areas of sediment supply and present and past transport of particles by water masses in the eastern Indian Ocean. Isotope signatures in surface sediments range from −21.5 (ɛNd), 0.8299 (87Sr/86Sr), and 19.89 (206Pb/204Pb) off northwest Australia to +0.7 (ɛNd), 0.7069 (87Sr/86Sr), and 17.44 (206Pb/204Pb) southwest of Java. The radiogenic isotope signatures primarily reflect petrographic characteristics of the surrounding continental bedrocks but are also influenced by weathering-induced grain size effects of Pb and Sr isotope systems with superimposed features that are caused by current transport of clay-sized particles, as evidenced off Australia where a peculiar isotopic signature characterizes sediments underlying the southward flowing Leeuwin Current and the northward flowing West Australian Current (WAC). Gravity core FR10/95-GC17 off west Australia recorded a major isotopic change from Last Glacial Maximum values of −10 (ɛNd), 0.745 (87Sr/86Sr), and 18.8 (206Pb/204Pb) to Holocene values of −22 (ɛNd), 0.8 (87Sr/86Sr), and 19.3 (206Pb/204Pb), which documents major climatically driven changes of the WAC and in local riverine particle supply from Australia during the past 20 kyr. In contrast, gravity core FR10/95-GC5 located below the present-day pathway of the Indonesian throughflow (ITF) shows a much smaller isotopic variability, indicating a relatively stable ITF hydrography over most of the past 92 kyr. Only the surface sediments differ significantly in their isotopic composition, indicating substantial changes in erosional sources attributed to a change of the current regime during the past 5 kyr.

Type: Article , PeerReviewed

Format: text

DOI: 10.1029/2011GC003544

Permalink