Björn Malmgren currently works at the Home Office, Solvägen 17, SE-761 64 Norrtälje, Sweden. Björn has been involved in research in the fields of marine micropaleontology, paleoceanography, paleoclimatology, climatology, microevolution, and the application of quantitative methods in the Earth sciences, including multivariate statistical analysis and artificial neural networks (ANNs). He has studied Neogene and latest Cretaceous marine sediments from wide areas of the globe. He has no major ongoing projects, since he retired in 2007. For further information, please refer to Google Scholar (https://scholar.google.se/citations?user=WRc7t1wAAAAJ&hl=sv) and Research Gate (https://www.researchgate.net/profile/Bjoern_Malmgren). Address: Solvägen 17 SE-761 64 Norrtälje Sweden
ABSTRACT Understanding natural climate variability on millennial and centennial time-scales is ne... more ABSTRACT Understanding natural climate variability on millennial and centennial time-scales is necessary for predicting future climate change. Here we present planktonic foraminiferal oxygen and carbon stable isotope records at decadal resolution from Santa Barbara Basin documenting California Current system variability through the Holocene. Threshold mean-climate changes in SSTs and upper-water column structure occurred as well as significant millennial- and centennial-scale variability. A transition from warmer SSTs and a more stratified water column to cooler SSTs and a less stratified water column occurred between 4 and 3 ka and is associated with a global climate transition exhibited in records from the tropics to the poles. Millennial and centennial oscillations in SST and water column structure are associated with inferred atmospheric variability in the tropics, North Atlantic and Antarctic. These results suggest that interdecadal-like teleconnections may have been active on centennial and millennial time-scales. Furthermore, centennial periodicities imbedded in the records suggest possible forcing through variations in solar output.
Most species of Late Cretaceous deep-sea benthic foraminifera are believed to be cosmopolitan and... more Most species of Late Cretaceous deep-sea benthic foraminifera are believed to be cosmopolitan and therefore to exhibit only minor biogeographical differences. In this preliminary report, six Deep Sea Drilling Project (DSDP) sites from different oceans, paleolatitudes, and paleodepths were analyzed for terminal Cretaceous abyssal-bathyal benthic foraminifera in order to investigate their assumed cosmopolitan distribution and the question of whether different faunal compositions are related to time, different paleolatitudes, and/or different paleodepths. The material studied was obtained from the low-latitude Site 465 (Pacific Ocean), and the intermediate-latitude Sites 384 (North Atlantic) and 356, 516, 525, and 527 (South Atlantic). The material analyzed represents a time slice encompassing the last 20-50 k.y. of the Cretaceous. The faunas contain numerous "Velasco-type" species, such as Gavelinella beccariiformis (White), Cibicidoides velascoensis (Cushman), Nuttallides truempyi (Nuttall), Gaudryina pyramidata Cushman, and various gyroidinoids and buliminids. The results contradict the general assumption of the cosmopolitan nature of Late Cretaceous deep-sea benthic foraminifera advocated in the literature. Only about 9% of the taxa identified were found to be truly "cosmopolitan" through their occurrence at all the sites analyzed. On the basis of correspondence analysis and relative abundance data, three assemblages and three subassemblages were recognized: (1) a bathyal-abyssal assemblage [Nuttallinella sp. A, Cibicidoides hyphalus (Fisher), Valvalabamina sp. evolute form, and Gyroidinoides spp.] at the South Atlantic Sites 356, 516, 525, and 527, divided into three subassemblages, namely (a) a middle bathyal subassemblage [Eouvigerina subsculptura McNeil and Caldwell, Truaxia aspera (Cushman), and G. pyramidata] at Sites 516 and 525, (b) a lower bathyal subassemblage [Osangularia? sp., Pyramidina rudita (Cushman and Parker), and Quadrimorphina camerata (Brotzen)] at Site 356, and (c) an abyssal subassemblage [...]
In the western Arabian Sea (WAS), the highest seasonal sea surface temperature (SST) difference p... more In the western Arabian Sea (WAS), the highest seasonal sea surface temperature (SST) difference presently occurs between May and August. In order to gain an understanding on how monsoonal upwelling modulates the SST difference between these two months, we have computed SST for the months of May and August based on census counts of planktonic foraminifers by using the artificial neural network (ANN) technique. The SST difference between May and August exhibits three distinct phases: i) a moderate SST difference in the late Holocene (0-3.5 ka) is attributable to intense upwelling during August, ii) a minimum SST difference from 4 to 12 ka is due to weak upwelling during the month of August, and iii) the highest SST difference during the last glacial interval (19 to 22 ka) with high Globigerina bulloides % could have been caused by the occurrence of a prolonged upwelling season (from May through July) and maximum difference in the incoming solar radiation between May and August. Overall, variations in the SST difference between May and August show that the timing of intense upwelling in the Western Arabian Sea over the last 22 kyr has been variable over the months of June, July and August.
The radiolarians and other microfossils have been widely used to estimate sea-surface temperature... more The radiolarians and other microfossils have been widely used to estimate sea-surface temperatures (SSTs) by the Imbrie-Kipp Transfer Function (IKTF) method, which evolved in 1971. Besides IKTF, the modern analog technique (MAT), artificial neural network (ANN), weighted-averaging partial least squares (WAPLS) regression, and maximum likelihood (ML) methods were used to estimate SSTs based on radiolarian fauna, and the accuracies associated with these methods were compared. Study suggested that the ANNs represent more optimum procedure for estimating SSTs than these other methods. Relative abundance (%) data for 38 modern radiolarian species in the core tops from the Pacific Ocean (Pisias et al., 1997) were first calibrated to measured February-April and August-October SSTs (World Ocean Data CD, 2001) by the ANNs and the other methods. Average root mean square error of prediction (RMSEP) for the ANNs is considerably lower (1.5° for February-April and 1.4° for August-October) in 10 independent hold-back (HB) test sets of observations, that were not part of the training of ANNs, than for the other methods (RMSEP ~2°) using the same split of training and test sets. Correlation coefficients between observed and estimated SSTs by the ANNs in 10-HB sets for both the February-April and August-October seasons are 0.98. Results suggest that the ANN-derived SSTs are ~25% and ~19% more accurate than those derived by the other methods during February-April and August-October seasons, respectively. Therefore, we estimated paleo-SSTs by the ANNs using same radiolarian species down core data in 10 sediment cores from the eastern equatorial Pacific (Pisias and Mix, 1997), and paleo-SST time series of the last ~800,000 years (~800-ka) were prepared. Besides, the ANN derived SST maps were made for the modern time, Last Glacial Maximum (LGM, ~23-ka), and Eemian (~125-ka) time-slices in the cores and analyzed. The ANN based SSTs suggested that the Peru upwelling was stronger during the LGM than at the modern and the Eemian times.
Ranking of differential dissolution of terminal Cretaceous calcareous nannofossils using a statis... more Ranking of differential dissolution of terminal Cretaceous calcareous nannofossils using a statistical approach
Shape measurements have been made on planktonic foraminifera from a South Pacific Late Miocene to... more Shape measurements have been made on planktonic foraminifera from a South Pacific Late Miocene to Recent temperate evolutionary lineage (Globorotalia conoidea through intermediate forms to G. inflata in DSDP Site 284). The sampling interval is about 0.1 Myr over nearly 8 Myr. Gradual evolution (phyletic gradualism) clearly occurs in all but one measured parameter. No clear evidence exists for abrupt evolutionary steps (punctuated equilibria) within the bioseries. If they occur, they are the exception rather than the rule. The number of chambers in the final whorl decreases almost linearly, despite known paleoceanographic oscillations within the temperate water mass. Mean size and apertural shape variations seem to correlate with paleoceanographic change. It is speculated that certain major morphological changes that took place within this evolutionary bioseries (i.e. loss of keel, rounding of periphery) developed in response to a major latest Miocene cooling, associated with instability in the water column and resulting adjustments of the test structure to water density changes. Changes exhibited in shape measurements may offer a precise method of stratigraphic correlation between temperate South Pacific Late Cenozoic sequences. Four species and two subspecies, long recognized to form the basis of this lineage, are redefined biometrically.
ABSTRACT A reconstruction is presented of major hurricane activity in the Atlantic region back to... more ABSTRACT A reconstruction is presented of major hurricane activity in the Atlantic region back to 1750. Almost all Atlantic major hurricanes (> 50 m/s; categories 3, 4, or 5 on the Saffir-Simpson hurricane scale) are developed in the area westward of Africa across the tropical Atlantic and Caribbean Sea at latitudes between 10N and 20N; an area termed the Main Development Region (MDR). They are developed through atmo- spheric easterly waves that propagate westward from Africa across the tropical North Atlantic. The magnitude of the vertical shear of the horizontal winds between the lower and upper troposphere |Vz| during August to October together with sea-surface temperatures (SSTs) in the MDR are the dominant factors controlling major hurricane activity. Local vertical wind shear |Vz| of > 8 m/s is unfavourable for development of major hurricanes due to prevention of the axisymmetric organisation of deep convec- tion. Local SSTs play a direct role in providing moist enthalpy to incipient hurricanes. Two proxies of tradewind variability from the Caribbean Sea derived from lumines- cence intensity in a coral core and abundance of the planktonic foraminifer Globige- rina bulloides in a sediment core, which are strongly correlated with |Vz| in MDR and major hurricane activity back to 1949 and 1944, respectively, are together with records of SSTs used to reconstruct major hurricane activity. The reconstruction indicates that the time interval from the late 1960s to early 1990s may have experienced strong |Vz| and few major hurricanes compared to other periods since 1750.
ABSTRACT Understanding natural climate variability on millennial and centennial time-scales is ne... more ABSTRACT Understanding natural climate variability on millennial and centennial time-scales is necessary for predicting future climate change. Here we present planktonic foraminiferal oxygen and carbon stable isotope records at decadal resolution from Santa Barbara Basin documenting California Current system variability through the Holocene. Threshold mean-climate changes in SSTs and upper-water column structure occurred as well as significant millennial- and centennial-scale variability. A transition from warmer SSTs and a more stratified water column to cooler SSTs and a less stratified water column occurred between 4 and 3 ka and is associated with a global climate transition exhibited in records from the tropics to the poles. Millennial and centennial oscillations in SST and water column structure are associated with inferred atmospheric variability in the tropics, North Atlantic and Antarctic. These results suggest that interdecadal-like teleconnections may have been active on centennial and millennial time-scales. Furthermore, centennial periodicities imbedded in the records suggest possible forcing through variations in solar output.
Most species of Late Cretaceous deep-sea benthic foraminifera are believed to be cosmopolitan and... more Most species of Late Cretaceous deep-sea benthic foraminifera are believed to be cosmopolitan and therefore to exhibit only minor biogeographical differences. In this preliminary report, six Deep Sea Drilling Project (DSDP) sites from different oceans, paleolatitudes, and paleodepths were analyzed for terminal Cretaceous abyssal-bathyal benthic foraminifera in order to investigate their assumed cosmopolitan distribution and the question of whether different faunal compositions are related to time, different paleolatitudes, and/or different paleodepths. The material studied was obtained from the low-latitude Site 465 (Pacific Ocean), and the intermediate-latitude Sites 384 (North Atlantic) and 356, 516, 525, and 527 (South Atlantic). The material analyzed represents a time slice encompassing the last 20-50 k.y. of the Cretaceous. The faunas contain numerous "Velasco-type" species, such as Gavelinella beccariiformis (White), Cibicidoides velascoensis (Cushman), Nuttallides truempyi (Nuttall), Gaudryina pyramidata Cushman, and various gyroidinoids and buliminids. The results contradict the general assumption of the cosmopolitan nature of Late Cretaceous deep-sea benthic foraminifera advocated in the literature. Only about 9% of the taxa identified were found to be truly "cosmopolitan" through their occurrence at all the sites analyzed. On the basis of correspondence analysis and relative abundance data, three assemblages and three subassemblages were recognized: (1) a bathyal-abyssal assemblage [Nuttallinella sp. A, Cibicidoides hyphalus (Fisher), Valvalabamina sp. evolute form, and Gyroidinoides spp.] at the South Atlantic Sites 356, 516, 525, and 527, divided into three subassemblages, namely (a) a middle bathyal subassemblage [Eouvigerina subsculptura McNeil and Caldwell, Truaxia aspera (Cushman), and G. pyramidata] at Sites 516 and 525, (b) a lower bathyal subassemblage [Osangularia? sp., Pyramidina rudita (Cushman and Parker), and Quadrimorphina camerata (Brotzen)] at Site 356, and (c) an abyssal subassemblage [...]
In the western Arabian Sea (WAS), the highest seasonal sea surface temperature (SST) difference p... more In the western Arabian Sea (WAS), the highest seasonal sea surface temperature (SST) difference presently occurs between May and August. In order to gain an understanding on how monsoonal upwelling modulates the SST difference between these two months, we have computed SST for the months of May and August based on census counts of planktonic foraminifers by using the artificial neural network (ANN) technique. The SST difference between May and August exhibits three distinct phases: i) a moderate SST difference in the late Holocene (0-3.5 ka) is attributable to intense upwelling during August, ii) a minimum SST difference from 4 to 12 ka is due to weak upwelling during the month of August, and iii) the highest SST difference during the last glacial interval (19 to 22 ka) with high Globigerina bulloides % could have been caused by the occurrence of a prolonged upwelling season (from May through July) and maximum difference in the incoming solar radiation between May and August. Overall, variations in the SST difference between May and August show that the timing of intense upwelling in the Western Arabian Sea over the last 22 kyr has been variable over the months of June, July and August.
The radiolarians and other microfossils have been widely used to estimate sea-surface temperature... more The radiolarians and other microfossils have been widely used to estimate sea-surface temperatures (SSTs) by the Imbrie-Kipp Transfer Function (IKTF) method, which evolved in 1971. Besides IKTF, the modern analog technique (MAT), artificial neural network (ANN), weighted-averaging partial least squares (WAPLS) regression, and maximum likelihood (ML) methods were used to estimate SSTs based on radiolarian fauna, and the accuracies associated with these methods were compared. Study suggested that the ANNs represent more optimum procedure for estimating SSTs than these other methods. Relative abundance (%) data for 38 modern radiolarian species in the core tops from the Pacific Ocean (Pisias et al., 1997) were first calibrated to measured February-April and August-October SSTs (World Ocean Data CD, 2001) by the ANNs and the other methods. Average root mean square error of prediction (RMSEP) for the ANNs is considerably lower (1.5° for February-April and 1.4° for August-October) in 10 independent hold-back (HB) test sets of observations, that were not part of the training of ANNs, than for the other methods (RMSEP ~2°) using the same split of training and test sets. Correlation coefficients between observed and estimated SSTs by the ANNs in 10-HB sets for both the February-April and August-October seasons are 0.98. Results suggest that the ANN-derived SSTs are ~25% and ~19% more accurate than those derived by the other methods during February-April and August-October seasons, respectively. Therefore, we estimated paleo-SSTs by the ANNs using same radiolarian species down core data in 10 sediment cores from the eastern equatorial Pacific (Pisias and Mix, 1997), and paleo-SST time series of the last ~800,000 years (~800-ka) were prepared. Besides, the ANN derived SST maps were made for the modern time, Last Glacial Maximum (LGM, ~23-ka), and Eemian (~125-ka) time-slices in the cores and analyzed. The ANN based SSTs suggested that the Peru upwelling was stronger during the LGM than at the modern and the Eemian times.
Ranking of differential dissolution of terminal Cretaceous calcareous nannofossils using a statis... more Ranking of differential dissolution of terminal Cretaceous calcareous nannofossils using a statistical approach
Shape measurements have been made on planktonic foraminifera from a South Pacific Late Miocene to... more Shape measurements have been made on planktonic foraminifera from a South Pacific Late Miocene to Recent temperate evolutionary lineage (Globorotalia conoidea through intermediate forms to G. inflata in DSDP Site 284). The sampling interval is about 0.1 Myr over nearly 8 Myr. Gradual evolution (phyletic gradualism) clearly occurs in all but one measured parameter. No clear evidence exists for abrupt evolutionary steps (punctuated equilibria) within the bioseries. If they occur, they are the exception rather than the rule. The number of chambers in the final whorl decreases almost linearly, despite known paleoceanographic oscillations within the temperate water mass. Mean size and apertural shape variations seem to correlate with paleoceanographic change. It is speculated that certain major morphological changes that took place within this evolutionary bioseries (i.e. loss of keel, rounding of periphery) developed in response to a major latest Miocene cooling, associated with instability in the water column and resulting adjustments of the test structure to water density changes. Changes exhibited in shape measurements may offer a precise method of stratigraphic correlation between temperate South Pacific Late Cenozoic sequences. Four species and two subspecies, long recognized to form the basis of this lineage, are redefined biometrically.
ABSTRACT A reconstruction is presented of major hurricane activity in the Atlantic region back to... more ABSTRACT A reconstruction is presented of major hurricane activity in the Atlantic region back to 1750. Almost all Atlantic major hurricanes (> 50 m/s; categories 3, 4, or 5 on the Saffir-Simpson hurricane scale) are developed in the area westward of Africa across the tropical Atlantic and Caribbean Sea at latitudes between 10N and 20N; an area termed the Main Development Region (MDR). They are developed through atmo- spheric easterly waves that propagate westward from Africa across the tropical North Atlantic. The magnitude of the vertical shear of the horizontal winds between the lower and upper troposphere |Vz| during August to October together with sea-surface temperatures (SSTs) in the MDR are the dominant factors controlling major hurricane activity. Local vertical wind shear |Vz| of > 8 m/s is unfavourable for development of major hurricanes due to prevention of the axisymmetric organisation of deep convec- tion. Local SSTs play a direct role in providing moist enthalpy to incipient hurricanes. Two proxies of tradewind variability from the Caribbean Sea derived from lumines- cence intensity in a coral core and abundance of the planktonic foraminifer Globige- rina bulloides in a sediment core, which are strongly correlated with |Vz| in MDR and major hurricane activity back to 1949 and 1944, respectively, are together with records of SSTs used to reconstruct major hurricane activity. The reconstruction indicates that the time interval from the late 1960s to early 1990s may have experienced strong |Vz| and few major hurricanes compared to other periods since 1750.
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.
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Papers by Björn A Malmgren