Björn A Malmgren | Home (original) (raw)
Papers by Björn A Malmgren
Marine Micropaleontology, Mar 1, 1987
... Nyong (1985) stated that absenceof strong bottom-water circulation in the Cre-taceous ocean p... more ... Nyong (1985) stated that absenceof strong bottom-water circulation in the Cre-taceous ocean prevented provincialism of ben-thonic foraminiferal faunas, but aided uniformand ... One might expect that the ar-eno-agglutinated benthonic foraminifers wouldbe resistant to dissolution. ...
Journal of Foraminiferal Research, 1996
ABSTRACT A high-resolution time-series analysis of the coiling properties of two planktic foramin... more ABSTRACT A high-resolution time-series analysis of the coiling properties of two planktic foraminiferal species, Neogloboquadrina pachyderma and Globigerina bulloides has been completed at ODP Site 723A, beneath the seasonal upwelling region of the Oman Margin in the Arabian Sea. Results indicate that accumulation rates of the sinistral morphotype of N. pachyderma increase during a period of strong upwelling between 10.5 and 5 Ka. The dextral morphotype of N. pachyderma shows greater values during the last glacial period when upwelling was relatively weak. Fluxes of both the sinistral and dextral morphotypes of G. bulloides increased during the interval of stronger upwelling. Greater increase in the flux of the sinistral than of the dextral morphotype of G. bulloides during this interval resulted in higher proportions of the sinistral morphotype in the sediment record. Enhanced flux of the sinistral morphotypes of N. pachyderma and G. bulloides during intensified upwelling suggests that the sinistral morphotypes of both taxa are more productive than the dextral morphotypes in the nutrient-rich upwelling waters. These patterns indicate that surface-water temperature may not be the only factor controlling coiling directions of N. pachyderma and G. bulloides.
A high-resolution (10-20 kyr) record of variations in CaCO3 content and dissolution was establish... more A high-resolution (10-20 kyr) record of variations in CaCO3 content and dissolution was established for latest Cretaceous (last 0.7 Myr) deep-sea sediments from the South Atlantic Ocean (DSDP Site 516 from the Rio Grande Rise, and sites 525 and 527 from the Walvis Ridge). The degree of fragmentation of planktonic foraminifera (DFP) was used as a measure of calcite dissolution. High negative correlations between DFP and other independent measures of carbonate dissolution (percentage of sand fraction, absolute abundance of planktonic foraminifera, and planktonic/benthic foraminiferal ratio) validate its use as a sensitive index of calcite dissolution in upper Maastrichtian deep-sea sediments.Very high DFP and a significant negative correlation between DFP and CaCO 3 content suggest that Site 516 was located below the foraminiferal lysocline during the entire interval studied. Such a shallow position of the lysocline (paleodepth of Site 516 was 1.2 km) may be explained by "upwelling" of corrosive deep waters along the southern margin of the Rio Grande Rise. Sites 525 and 527 were located above the foraminiferal lysocline; however, three short periods of enhanced dissolution were recognised at Site 525 (paleodepth 1 km) and one interval of strong dissolution was identified at Site 527 (paleodepth 2.7 km). The lack of correspondence between the dissolution regimes at sites from the Walvis Ridge suggests limited deep-water communication across this physiographic barrier. Two of the dissolution maxima recognised at Site 525 correspond to carbonate maxima at Site 527. Variations in "upwelling" intensity along the Walvis Ridge, resulting in fluctuations in primary productivity in this area, may be the proximal cause of both carbonate cycles at Site 527 and dissolution cycles at Site 525. We suggest that development of the bottom Ekman layer between a hypothetical westward geostrophic current and the topographical height of the Rio Grande Rise-Walvis Ridge system may be a plausible hydrodynamical explanation for the propos [...]
We have carried out a high-resolution study of fluctuations in upwelling intensity along the Oman... more We have carried out a high-resolution study of fluctuations in upwelling intensity along the Oman Margin, western Arabian Sea, through the last 19,130 years based on several marine microfossil indices of upwelling. We document a periodicity of 2,200 years in the upwelling indices, which would be governed by the south-west (SW) monsoon with such a periodicity. Our data further demonstrate greater amplitude in the variability of the SW monsoon during the Holocene than during the last glacial period. Our reported 2,200 years periodicity has two implications (1) oceanic circulation changes partly influence monsoon strength at sub-Milankovitch cycles (2) previously documented 2,300 years periodicity in atmospheric 14C might be induced by oceanic circulation changes.
Annual, summer, and winter sea surface temperatures (SSTs) in the western Arabian Sea were recons... more Annual, summer, and winter sea surface temperatures (SSTs) in the western Arabian Sea were reconstructed through the last 22 kyr using artificial neural networks (ANNs) based on quantitative analyses of planktic foraminifera. Down-core SST estimates reveal that annual, summer, and winter SSTs were 2, 1.2, and 2.6°C cooler, respectively, during the last glacial period than in the Holocene. A 2.5°C SST increase during Termination 1A (hereinafter referred as glacial to Holocene transition) in the western Arabian Sea. The study reveals a strong seasonal SST contrast between winter and summer from 18 to 14 calendar kyr owing to the combined effect of weak upwelling and strong cold northeasterly winds. Minor or no seasonal SST changes were noticed within the Holocene period, which is attributed to the intense upwelling during the summer monsoon. This causes a lowering of SST to values similar to those of the winter season in analogy with the present day. A 3°C rise in winter SSTs during the glacial to Holocene transition coincides with a strengthening of the monsoon, suggesting a link between winter SST and monsoon initiation from the beginning of the Holocene. Strikingly, annual, summer, and winter SSTs show a cooling trend from ~8 ka to the present day, implying tropical cooling in the late Holocene.
Biogeographic patterns in terminal Cretaceous planktonic foraminifera have been analyzed from the... more Biogeographic patterns in terminal Cretaceous planktonic foraminifera have been analyzed from their faunal compositions at a time-slice spanning the upper parts of the calcareous nannofossil Micula prinsii Zone (approximately the latest 20-60 k.y. of the Cretaceous) at DSDP sites from low ( 16° ) through middle (37° ) paleolatitudes in either the Northern or the Southern Hemisphere. The study is based on relative abundance data of 26 species at Sites 356, 516F, 525A and 527 from the South Atlantic Ocean, Sites 384 and 548A from the North Atlantic and Sites 465A and 577A from the North Pacific. Cretaceous-Tertiary (K-T) boundary sections at Site 516F and 577A are poorly preserved, which prevented quantitative faunal analysis.
Two major faunal assemblages, one Tethyan Assemblage and one Transitional Assemblage, are distinguished from the quantitative distribution patterns. The Tethyan Assemblage, dominating at Sites 465A, 356 and 384, is composed of Het- erohelix striata, Globotruncana aegyptiaca, Pseudoguembelina kempensis, P. costulata, an undescribed form of Heterohelix with relict apertural flanges along medium suture, Rugoglobigerina hexacamerata and Trinitella scotti. Among these spe- cies P. kempensis, P. costulata and H. sp. exhibit enhanced abundances at Site 465A and constitute a Warm Tethyan Subassemblage, whereas R. hexacamerata and T. scotti, which are most abundant at Sites 356 and 384, represent a Cool Tethyan Subassemblage. Seven species show greater relative abundances at Sites 525A and 527 and are referred to a Warm Transitional Subassemblage: Abathomphalus mayaroensis, Gublerina cuvillieri, Pseudotextularia elegans, Rugoglobigerina rugosa, Racemiguembelina fructicosa, Globotruncana arca and Planoglobulina acervulinoides. In addition, an assemblage, marked by the Heterohelix glabrans-H, carinata complex, H. globulosa, GlobigerineUoides multispina and Rosita contusa,
may represent a "shallower-water" subassemblage within warm Transitional waters (Site 548A).
Palaeogeography, Palaeoclimatology, Palaeoecology, 2003
Daily rainfall data for 187 stations in Sri Lanka spanning the period 1960-1996 were analyzed to ... more Daily rainfall data for 187 stations in Sri Lanka spanning the period 1960-1996 were analyzed to investigate the spatial and temporal characteristics of the mean rainfall intensity (MRI) through this time interval with special focus on the Southwest Monsoon (May^September). Particular emphasis was laid on temporal changes in the MRI series. The mean and standard deviation (SD) of the MRI data showed considerable spatial variation. Regression analysis expressing precipitation as a function of time at the various stations revealed distinct spatial trends; the results point to high MRI in lowland areas and low MRI in mountain areas. Principal Components Analysis of the temporal relationships among a reduced set of stations located in an equal-sized grid showed that the three dominant principal components (PCs) are characterized by the maximum and minimum mean and SD of the MRI series together with the mean number of rainy days. The first, second and third PC modes show significant patterns of the MRI data series over the northern half, southern half and southwestern coastal belt of Sri Lanka, respectively. The time series pattern of the dominant PC modes revealed distinct changes in MRI over time. A noticeable higher value in MRI was found from 1977 to 1996; this tendency is most pronounced for the first PC mode. The time series of the Southern Oscillation Index was found to be closely related to changes in the MRI patterns associated with the first PC mode. In addition, El Nino years coincide with low values of the first PC mode. Some La Nina years show a positive response for the first and third PC modes, while there is no clear response for the MRI pattern identified by the second PC.
Journal of Geophysical Research, 2007
Thirty-five meteorological stations encompassing the Caribbean region (Cuba, Bahamas, Jamaica, D... more Thirty-five meteorological stations encompassing the Caribbean region (Cuba,
Bahamas, Jamaica, Dominican Republic, Puerto Rico, US Virgin Islands, St. Maarten,
and Barbados) were analyzed over the time interval 1951–1981 to assess regional
precipitation patterns and their relationships with the North Atlantic Oscillation (NAO)
and El Nino-Southern Oscillation (ENSO). Application of factor analysis to
these series revealed the existence of four geographically distinct precipitation
regions, (C1) western Cuba and northwestern Bahamas, (C2) Jamaica, eastern Cuba,
and southeastern Bahamas, (C3) Dominican Republic and northwestern Puerto Rico,
and (C4) eastern Puerto Rico, US Virgin Islands, St. Maarten, and Barbados. This
regionalization is related to different annual cycles and interannual fluctuations of rainfall.
The annual cycle is more unimodal and largest in the northwest Caribbean (C1) and
becomes increasingly bimodal toward lower latitudes (C4) as expected. Year-to-year
variations of precipitation are compared with two well-known climatic indices. The ENSO relationship, represented by Nin˜o 3.4 sea surface temperatures (SST), is positive and stable at all lags, but tends to reverse over the SE Caribbean (C4) in late summer.
The NAO influence is weak and seasonally dependent. Early summer rainfall in the
northwest Caribbean (C1) increases under El Nin˜o conditions. Clusters 2 and 3 are less influenced by the global predictors and more regional in character.
Marine Micropaleontology, 2011
Palaeogeography, Palaeoclimatology, Palaeoecology, Oct 1, 1973
Planktonic foraminiferal assemblages from 32 surface sediment samples from high latitudes of the ... more Planktonic foraminiferal assemblages from 32 surface sediment samples from high latitudes of the South Pacific Ocean have been subjected to a multivariate statistical classification method termed "principal coordinates analysis". On the basis of the presence or absence of 18 species of planktonic Foraminifera, and the frequency and coiling direction of the cold-water species Globigerina pachyderma, the samples were clustered into five groups, where one group represents the subtropical, two the subantarctic, and two the Antarctic water mass. This assemblage-grouping method is suitable for investigations of past climatic changes.
Journal of the International Association for Mathematical Geology, Jun 1, 1979
Data of a microfossil group, the planktonic foraminifera, have been tested to determine the confo... more Data of a microfossil group, the planktonic foraminifera, have been tested to determine the conformity of various real data distributions to univariate and multivariate normality and the effects that standard transformations have upon the distributions. Studies of two bivariate samples, one trivariate sample, and two quadrivariate samples of size data indicate that distributions frequently deviate greatly from multivariate normality. Univariate distributions are generally positively skewed and show a tendency for leptokurtosis. A logarithmic transformation improved both univariate and multivariate distributions but the number of distributions conformable to normality increased only slightly-from zero to one in the multivariate case and from one to four in the univariate case (totally 15 distributions). Aresine (p/lO0) ~ transformations of percentage data in two samples including 16 and 23 species, respectively, decreased highly significant deviations from multivariate normality but distributions remained greatly non-normal. Although markedly positively skewed and leptokurtic univariate distributions were improved in most instances, the number of normal distributions (two) did not change. It follows that neither of the transformations caused significant increases in the number of normal distributions but if it is assumed that the consequences of non-normality are less severe as the deviation from normality decreases, the transformations are justified.
Marine Micropaleontology, Dec 1, 1983
ABSTRACT
Journal of Foraminiferal Research, Apr 1, 1992
The extinctions linked to the Cretaceous/Tertiary (K/T) boundary event and their causes have rece... more The extinctions linked to the Cretaceous/Tertiary (K/T) boundary event and their causes have recently attracted a great deal of attention. In order to determine how the deep-sea benthic foraminifera responded to this event, changes in diversity and quantitative composition of this group acrnss the WT boundary were analyzed at three Deep Sea Drilling Project (DSDP) sites from different paleodepths and paleolatitudes: the Pacific Site 465 (Hess Rise; paleodepth 1,500 m; paleolatitude: 16ON) and two South Atlantic sites from the same paleolatitude (363): Sites 525 (Walvis Ridge; paleodepth 1,100 m) and 527 (Angola Basin; paleodepth 2,700 m). The sections analyzed span between 400 and 450 ky across the WT boundary. A total of 149 benthic foraminiferal taxa were identified at the generic or specific level. Percentages nf taxonomic disappearances varied between 13 and 40% when the maximum percentages of disappearances of Maestrichtian taxa in the Danian samples were considered, and between 5 and 23% when only those taxa were included that were present in at least 50% of the Danian or Maestrichtian samples. The taxonomic disappearances were more than twice as high (40 and 23%, respectively) at the shallower South Atlantic Site 525 as compared to the deeper Site 527 (18 and 9%, respectively). This suggests that the disappearances of taxa are paleobathymetrically controlled at middle latitudes in the South Atlantic. Furthermore, the low-latitude Site 465 showed lower degrees of disappearances (13 and s%, respectively) than the higher-latitude Sites 525 and 527. This suggests that there is a paleolatitudinal control of the taxonomic disappearances in benthic foraminifera across the WT boundary. Taxnnomic diversity (number of taxa per sample standardized to a sample size of 100 using Hurlbert's diversity index) started to increase 101-150 ky below the K/T boundary at both the South Atlantic Sites 525 and 527 and reached a maximum &50 ky below the WT boundary. The increase was from 29 to 40 taxa at Site 525, and from 26 to 39 taxa at Site 527. At the Pacific Site 465, there was no significant change in diversity prior to the WT boundary and the S(100) values varied between 23 and 27 taxa during the Maestrichtian. During the first 150 ky of the earliest Danian, diversity decreased at all three sites to 28, 33, and 18 taxa at Sites 525, 527, and 465, respectively. Results support the hypothesis that deep-sea benthic foraminifera were not severely affected by the WT tran
Marine Micropaleontology, Mar 1, 1987
... Nyong (1985) stated that absenceof strong bottom-water circulation in the Cre-taceous ocean p... more ... Nyong (1985) stated that absenceof strong bottom-water circulation in the Cre-taceous ocean prevented provincialism of ben-thonic foraminiferal faunas, but aided uniformand ... One might expect that the ar-eno-agglutinated benthonic foraminifers wouldbe resistant to dissolution. ...
Journal of Foraminiferal Research, 1996
ABSTRACT A high-resolution time-series analysis of the coiling properties of two planktic foramin... more ABSTRACT A high-resolution time-series analysis of the coiling properties of two planktic foraminiferal species, Neogloboquadrina pachyderma and Globigerina bulloides has been completed at ODP Site 723A, beneath the seasonal upwelling region of the Oman Margin in the Arabian Sea. Results indicate that accumulation rates of the sinistral morphotype of N. pachyderma increase during a period of strong upwelling between 10.5 and 5 Ka. The dextral morphotype of N. pachyderma shows greater values during the last glacial period when upwelling was relatively weak. Fluxes of both the sinistral and dextral morphotypes of G. bulloides increased during the interval of stronger upwelling. Greater increase in the flux of the sinistral than of the dextral morphotype of G. bulloides during this interval resulted in higher proportions of the sinistral morphotype in the sediment record. Enhanced flux of the sinistral morphotypes of N. pachyderma and G. bulloides during intensified upwelling suggests that the sinistral morphotypes of both taxa are more productive than the dextral morphotypes in the nutrient-rich upwelling waters. These patterns indicate that surface-water temperature may not be the only factor controlling coiling directions of N. pachyderma and G. bulloides.
A high-resolution (10-20 kyr) record of variations in CaCO3 content and dissolution was establish... more A high-resolution (10-20 kyr) record of variations in CaCO3 content and dissolution was established for latest Cretaceous (last 0.7 Myr) deep-sea sediments from the South Atlantic Ocean (DSDP Site 516 from the Rio Grande Rise, and sites 525 and 527 from the Walvis Ridge). The degree of fragmentation of planktonic foraminifera (DFP) was used as a measure of calcite dissolution. High negative correlations between DFP and other independent measures of carbonate dissolution (percentage of sand fraction, absolute abundance of planktonic foraminifera, and planktonic/benthic foraminiferal ratio) validate its use as a sensitive index of calcite dissolution in upper Maastrichtian deep-sea sediments.Very high DFP and a significant negative correlation between DFP and CaCO 3 content suggest that Site 516 was located below the foraminiferal lysocline during the entire interval studied. Such a shallow position of the lysocline (paleodepth of Site 516 was 1.2 km) may be explained by "upwelling" of corrosive deep waters along the southern margin of the Rio Grande Rise. Sites 525 and 527 were located above the foraminiferal lysocline; however, three short periods of enhanced dissolution were recognised at Site 525 (paleodepth 1 km) and one interval of strong dissolution was identified at Site 527 (paleodepth 2.7 km). The lack of correspondence between the dissolution regimes at sites from the Walvis Ridge suggests limited deep-water communication across this physiographic barrier. Two of the dissolution maxima recognised at Site 525 correspond to carbonate maxima at Site 527. Variations in "upwelling" intensity along the Walvis Ridge, resulting in fluctuations in primary productivity in this area, may be the proximal cause of both carbonate cycles at Site 527 and dissolution cycles at Site 525. We suggest that development of the bottom Ekman layer between a hypothetical westward geostrophic current and the topographical height of the Rio Grande Rise-Walvis Ridge system may be a plausible hydrodynamical explanation for the propos [...]
We have carried out a high-resolution study of fluctuations in upwelling intensity along the Oman... more We have carried out a high-resolution study of fluctuations in upwelling intensity along the Oman Margin, western Arabian Sea, through the last 19,130 years based on several marine microfossil indices of upwelling. We document a periodicity of 2,200 years in the upwelling indices, which would be governed by the south-west (SW) monsoon with such a periodicity. Our data further demonstrate greater amplitude in the variability of the SW monsoon during the Holocene than during the last glacial period. Our reported 2,200 years periodicity has two implications (1) oceanic circulation changes partly influence monsoon strength at sub-Milankovitch cycles (2) previously documented 2,300 years periodicity in atmospheric 14C might be induced by oceanic circulation changes.
Annual, summer, and winter sea surface temperatures (SSTs) in the western Arabian Sea were recons... more Annual, summer, and winter sea surface temperatures (SSTs) in the western Arabian Sea were reconstructed through the last 22 kyr using artificial neural networks (ANNs) based on quantitative analyses of planktic foraminifera. Down-core SST estimates reveal that annual, summer, and winter SSTs were 2, 1.2, and 2.6°C cooler, respectively, during the last glacial period than in the Holocene. A 2.5°C SST increase during Termination 1A (hereinafter referred as glacial to Holocene transition) in the western Arabian Sea. The study reveals a strong seasonal SST contrast between winter and summer from 18 to 14 calendar kyr owing to the combined effect of weak upwelling and strong cold northeasterly winds. Minor or no seasonal SST changes were noticed within the Holocene period, which is attributed to the intense upwelling during the summer monsoon. This causes a lowering of SST to values similar to those of the winter season in analogy with the present day. A 3°C rise in winter SSTs during the glacial to Holocene transition coincides with a strengthening of the monsoon, suggesting a link between winter SST and monsoon initiation from the beginning of the Holocene. Strikingly, annual, summer, and winter SSTs show a cooling trend from ~8 ka to the present day, implying tropical cooling in the late Holocene.
Biogeographic patterns in terminal Cretaceous planktonic foraminifera have been analyzed from the... more Biogeographic patterns in terminal Cretaceous planktonic foraminifera have been analyzed from their faunal compositions at a time-slice spanning the upper parts of the calcareous nannofossil Micula prinsii Zone (approximately the latest 20-60 k.y. of the Cretaceous) at DSDP sites from low ( 16° ) through middle (37° ) paleolatitudes in either the Northern or the Southern Hemisphere. The study is based on relative abundance data of 26 species at Sites 356, 516F, 525A and 527 from the South Atlantic Ocean, Sites 384 and 548A from the North Atlantic and Sites 465A and 577A from the North Pacific. Cretaceous-Tertiary (K-T) boundary sections at Site 516F and 577A are poorly preserved, which prevented quantitative faunal analysis.
Two major faunal assemblages, one Tethyan Assemblage and one Transitional Assemblage, are distinguished from the quantitative distribution patterns. The Tethyan Assemblage, dominating at Sites 465A, 356 and 384, is composed of Het- erohelix striata, Globotruncana aegyptiaca, Pseudoguembelina kempensis, P. costulata, an undescribed form of Heterohelix with relict apertural flanges along medium suture, Rugoglobigerina hexacamerata and Trinitella scotti. Among these spe- cies P. kempensis, P. costulata and H. sp. exhibit enhanced abundances at Site 465A and constitute a Warm Tethyan Subassemblage, whereas R. hexacamerata and T. scotti, which are most abundant at Sites 356 and 384, represent a Cool Tethyan Subassemblage. Seven species show greater relative abundances at Sites 525A and 527 and are referred to a Warm Transitional Subassemblage: Abathomphalus mayaroensis, Gublerina cuvillieri, Pseudotextularia elegans, Rugoglobigerina rugosa, Racemiguembelina fructicosa, Globotruncana arca and Planoglobulina acervulinoides. In addition, an assemblage, marked by the Heterohelix glabrans-H, carinata complex, H. globulosa, GlobigerineUoides multispina and Rosita contusa,
may represent a "shallower-water" subassemblage within warm Transitional waters (Site 548A).
Palaeogeography, Palaeoclimatology, Palaeoecology, 2003
Daily rainfall data for 187 stations in Sri Lanka spanning the period 1960-1996 were analyzed to ... more Daily rainfall data for 187 stations in Sri Lanka spanning the period 1960-1996 were analyzed to investigate the spatial and temporal characteristics of the mean rainfall intensity (MRI) through this time interval with special focus on the Southwest Monsoon (May^September). Particular emphasis was laid on temporal changes in the MRI series. The mean and standard deviation (SD) of the MRI data showed considerable spatial variation. Regression analysis expressing precipitation as a function of time at the various stations revealed distinct spatial trends; the results point to high MRI in lowland areas and low MRI in mountain areas. Principal Components Analysis of the temporal relationships among a reduced set of stations located in an equal-sized grid showed that the three dominant principal components (PCs) are characterized by the maximum and minimum mean and SD of the MRI series together with the mean number of rainy days. The first, second and third PC modes show significant patterns of the MRI data series over the northern half, southern half and southwestern coastal belt of Sri Lanka, respectively. The time series pattern of the dominant PC modes revealed distinct changes in MRI over time. A noticeable higher value in MRI was found from 1977 to 1996; this tendency is most pronounced for the first PC mode. The time series of the Southern Oscillation Index was found to be closely related to changes in the MRI patterns associated with the first PC mode. In addition, El Nino years coincide with low values of the first PC mode. Some La Nina years show a positive response for the first and third PC modes, while there is no clear response for the MRI pattern identified by the second PC.
Journal of Geophysical Research, 2007
Thirty-five meteorological stations encompassing the Caribbean region (Cuba, Bahamas, Jamaica, D... more Thirty-five meteorological stations encompassing the Caribbean region (Cuba,
Bahamas, Jamaica, Dominican Republic, Puerto Rico, US Virgin Islands, St. Maarten,
and Barbados) were analyzed over the time interval 1951–1981 to assess regional
precipitation patterns and their relationships with the North Atlantic Oscillation (NAO)
and El Nino-Southern Oscillation (ENSO). Application of factor analysis to
these series revealed the existence of four geographically distinct precipitation
regions, (C1) western Cuba and northwestern Bahamas, (C2) Jamaica, eastern Cuba,
and southeastern Bahamas, (C3) Dominican Republic and northwestern Puerto Rico,
and (C4) eastern Puerto Rico, US Virgin Islands, St. Maarten, and Barbados. This
regionalization is related to different annual cycles and interannual fluctuations of rainfall.
The annual cycle is more unimodal and largest in the northwest Caribbean (C1) and
becomes increasingly bimodal toward lower latitudes (C4) as expected. Year-to-year
variations of precipitation are compared with two well-known climatic indices. The ENSO relationship, represented by Nin˜o 3.4 sea surface temperatures (SST), is positive and stable at all lags, but tends to reverse over the SE Caribbean (C4) in late summer.
The NAO influence is weak and seasonally dependent. Early summer rainfall in the
northwest Caribbean (C1) increases under El Nin˜o conditions. Clusters 2 and 3 are less influenced by the global predictors and more regional in character.
Marine Micropaleontology, 2011
Palaeogeography, Palaeoclimatology, Palaeoecology, Oct 1, 1973
Planktonic foraminiferal assemblages from 32 surface sediment samples from high latitudes of the ... more Planktonic foraminiferal assemblages from 32 surface sediment samples from high latitudes of the South Pacific Ocean have been subjected to a multivariate statistical classification method termed "principal coordinates analysis". On the basis of the presence or absence of 18 species of planktonic Foraminifera, and the frequency and coiling direction of the cold-water species Globigerina pachyderma, the samples were clustered into five groups, where one group represents the subtropical, two the subantarctic, and two the Antarctic water mass. This assemblage-grouping method is suitable for investigations of past climatic changes.
Journal of the International Association for Mathematical Geology, Jun 1, 1979
Data of a microfossil group, the planktonic foraminifera, have been tested to determine the confo... more Data of a microfossil group, the planktonic foraminifera, have been tested to determine the conformity of various real data distributions to univariate and multivariate normality and the effects that standard transformations have upon the distributions. Studies of two bivariate samples, one trivariate sample, and two quadrivariate samples of size data indicate that distributions frequently deviate greatly from multivariate normality. Univariate distributions are generally positively skewed and show a tendency for leptokurtosis. A logarithmic transformation improved both univariate and multivariate distributions but the number of distributions conformable to normality increased only slightly-from zero to one in the multivariate case and from one to four in the univariate case (totally 15 distributions). Aresine (p/lO0) ~ transformations of percentage data in two samples including 16 and 23 species, respectively, decreased highly significant deviations from multivariate normality but distributions remained greatly non-normal. Although markedly positively skewed and leptokurtic univariate distributions were improved in most instances, the number of normal distributions (two) did not change. It follows that neither of the transformations caused significant increases in the number of normal distributions but if it is assumed that the consequences of non-normality are less severe as the deviation from normality decreases, the transformations are justified.
Marine Micropaleontology, Dec 1, 1983
ABSTRACT
Journal of Foraminiferal Research, Apr 1, 1992
The extinctions linked to the Cretaceous/Tertiary (K/T) boundary event and their causes have rece... more The extinctions linked to the Cretaceous/Tertiary (K/T) boundary event and their causes have recently attracted a great deal of attention. In order to determine how the deep-sea benthic foraminifera responded to this event, changes in diversity and quantitative composition of this group acrnss the WT boundary were analyzed at three Deep Sea Drilling Project (DSDP) sites from different paleodepths and paleolatitudes: the Pacific Site 465 (Hess Rise; paleodepth 1,500 m; paleolatitude: 16ON) and two South Atlantic sites from the same paleolatitude (363): Sites 525 (Walvis Ridge; paleodepth 1,100 m) and 527 (Angola Basin; paleodepth 2,700 m). The sections analyzed span between 400 and 450 ky across the WT boundary. A total of 149 benthic foraminiferal taxa were identified at the generic or specific level. Percentages nf taxonomic disappearances varied between 13 and 40% when the maximum percentages of disappearances of Maestrichtian taxa in the Danian samples were considered, and between 5 and 23% when only those taxa were included that were present in at least 50% of the Danian or Maestrichtian samples. The taxonomic disappearances were more than twice as high (40 and 23%, respectively) at the shallower South Atlantic Site 525 as compared to the deeper Site 527 (18 and 9%, respectively). This suggests that the disappearances of taxa are paleobathymetrically controlled at middle latitudes in the South Atlantic. Furthermore, the low-latitude Site 465 showed lower degrees of disappearances (13 and s%, respectively) than the higher-latitude Sites 525 and 527. This suggests that there is a paleolatitudinal control of the taxonomic disappearances in benthic foraminifera across the WT boundary. Taxnnomic diversity (number of taxa per sample standardized to a sample size of 100 using Hurlbert's diversity index) started to increase 101-150 ky below the K/T boundary at both the South Atlantic Sites 525 and 527 and reached a maximum &50 ky below the WT boundary. The increase was from 29 to 40 taxa at Site 525, and from 26 to 39 taxa at Site 527. At the Pacific Site 465, there was no significant change in diversity prior to the WT boundary and the S(100) values varied between 23 and 27 taxa during the Maestrichtian. During the first 150 ky of the earliest Danian, diversity decreased at all three sites to 28, 33, and 18 taxa at Sites 525, 527, and 465, respectively. Results support the hypothesis that deep-sea benthic foraminifera were not severely affected by the WT tran
Artificial neural networks (ANNs) have been recently applied for estimating past summer and winte... more Artificial neural networks (ANNs) have been recently applied for estimating past summer and winter sea-surface water temperatures (SST) from planktonic foraminifer relative-abundance data from the Atlantic and Indian oceans. ANNs are computer systems that have the ability to "learn" the relationship between a set of input vectors (faunal data) and one or several output vectors (SST data). This "learning" is accomplished through an algorithm that gradually adjusts the structure of the network in order to minimize the error between the target vector and network output. An attempt has now been made to apply the ANN technique for paleotemperature predictions from di-atom relative-abundance data of 61 species from the Atlantic Ocean, applicable to the 0-10 m water-depth interval. Two-thirds of the available samples (195 samples) were used for training of the neural networks, and the remaining one-third of the samples was employed for testing their performance (prediction error in terms of root-mean squared errors of prediction, RMSEPs). Six independent runs were made for each of the summer and winter SSTs to assess the stability of the RMSEPs using different training-and test-set partitions. The average RMSEP is 1.29 degrees C for summer SST and 1.60 degrees C for winter SST (the average correlation between actual and predicted SSTs is 0.988 for summer SST and 0.986 for winter SST), suggesting that this technique holds much promise for estimates of past SSTs. Of particular significance is the ability of the diatom-based ANNs to well predict SSTs below 5 and above 25 degrees C.