Contrasting vertical distributions of recent planktic foraminifera off Indonesia during the southeast monsoon: implications for paleoceanographic reconstructions

Planktic foraminifera are widely used in palaeoceanographic and paleoclimatic studies. The accuracy of such reconstructions depends on our understanding of the organisms’ ecology. Here we report on field observations of planktic foraminiferal abundances (>150 µm) from 5 depth intervals between 0–500 m water depth at 37 sites in the eastern tropical Indian Ocean. The total planktic foraminiferal assemblage comprises 29 morphospecies; with 11 morphospecies accounting for ~90 % of the total assemblage. Both species composition and dominance in the net samples are broadly consistent with the published data from the corresponding surface sediments. The abundance and vertical distribution of planktic foraminifera are low offshore west Sumatra, and increase towards offshore south Java and the Lesser Sunda Islands (LSI). Average living depth of Trilobatus trilobus, Globigerinoides ruber, and Globigerina bulloides increases eastward, while that of Neogloboquadrina dutertrei, Pulleniatina obliquiloculata, and Globorotalia menardii remains constant. We interpret the overall zonal and vertical distribution patterns in planktic foraminiferal abundances as a response to the contrasting upper water column conditions during the southeast monsoon, i.e., oligotrophic and stratified offshore Sumatra (non-upwelling) vs. eutrophic and well-mixed offshore Java-LSI (upwelling). Overall, the inferred habitat depths of selected planktic foraminifera species show a good agreement with those from sediment trap samples and from surface sedimentss off Sumatra, but not with those from surface sediments off Java-LSI. The discrepancy might stem from the different temporal coverage of these sample types. Our findings highlight the need to consider how foraminiferal assemblages and ecology vary on shorter timescales, i.e., from “snapshots” of the water column captured by plankton net to seasonal and interannual variability as recorded in sediment traps and how these changes are transferred and preserved in deep-sea sediments.

Planktic Foraminifera-Based Sea Surface Temperature Estimates and Late Quaternary Oceanography off New Zealand's West Coast

<p>Planktic foraminiferal assemblages were used to investigate the paleoceanography of the Eastern Tasman Sea over the last 480 kyrs (Marine Isotope Stages 12-1). One hundred and sixty-two faunas (96 picked and identified as part of this project (MIS 12-6) added to 66 census counts from Dr. M. Crundwell (MIS 6-1)) have been assembled from Marion Dufresne piston core MD06-2986 (~43˚ S. off New Zealand‟s west coast, 1477 m water depth). Faunal changes through the last five glacial-interglacial cycles are used to track surface water mass movement. Glacial periods are dominated by the eutrophic species Globigerina bulloides, with significant contributions from the temperate species Globoconella inflata. Temperate species Neogloboquadrina incompta and Gc. inflata dominate interglacials, with the former dominating the warmer parts and the latter dominating the cooler parts of the interglacials. Modern Analogue Technique (MAT) and an Artificial Neural Network (ANN) were used to estimate past sea surface temperatures (SST) based on the foraminiferal census counts data (23 species, ~46,000 specimens). SSTs show that MIS 12 was the longest, sustained cold period, while the coldest temperature was recorded in MIS 5d (~8º C). Interglacials MIS 11 and 5e are the two warmest stages of the record, with SSTs reaching ~18.5º C, about ~2º C warmer than present day. We find that contrary to either the western Tasman Sea or offshore eastern New Zealand, the eastern Tasman Sea has been fairly isolated from any major influx of subpolar or subtropical species carried in with surface water from either high or low latitude sources. Subtropical taxa abundance (Globigerinoides ruber, Neogloboquadrina dutertrei (D), Globigerinoides sacculifer, Globigerinella aequilateralis, Sphaeroidinellopsis dehiscens, Truncorotalia truncatulinoides (D), Beella digitata) is low (average ~0.6%) and only prominent during peak interglacials. Subantarctic taxa abundance (Neogloboquadrina pachyderma, Neogloboquadrina dutertrei (S)) is low (average ~5.1%), but significant, particularly in glacial periods. Comparison of faunal and SSTANN data along with ratios of Nq. pachyderma:Nq. incompta (previously referred to as coiling ratios of Nq. pachyderma) and absolute abundance of planktic productivity (a productivity proxy) suggest that the STF migrated northwards towards the site in all glacial periods, and may have moved over the site in MIS 12 and possibly MIS 5d. A latitudinal SSTANN 25 comparison between offshore eastern and western New Zealand reveals that MD06-2986 (~43º S) is most similar (~0.5º C) to ODP Site 1125 (~42º S). On the contrary, ODP Site 1119 (44º S) is ~5º C cooler than MD06-2986. This comparison highlights the significant changes in surface water masses off eastern New Zealand that exist in such a short span of latitude because of the influence of a complex submarine topography.</p>

Planktic Foraminifera-Based Sea Surface Temperature Estimates and Late Quaternary Oceanography off New Zealand's West Coast

<p>Planktic foraminiferal assemblages were used to investigate the paleoceanography of the Eastern Tasman Sea over the last 480 kyrs (Marine Isotope Stages 12-1). One hundred and sixty-two faunas (96 picked and identified as part of this project (MIS 12-6) added to 66 census counts from Dr. M. Crundwell (MIS 6-1)) have been assembled from Marion Dufresne piston core MD06-2986 (~43˚ S. off New Zealand‟s west coast, 1477 m water depth). Faunal changes through the last five glacial-interglacial cycles are used to track surface water mass movement. Glacial periods are dominated by the eutrophic species Globigerina bulloides, with significant contributions from the temperate species Globoconella inflata. Temperate species Neogloboquadrina incompta and Gc. inflata dominate interglacials, with the former dominating the warmer parts and the latter dominating the cooler parts of the interglacials. Modern Analogue Technique (MAT) and an Artificial Neural Network (ANN) were used to estimate past sea surface temperatures (SST) based on the foraminiferal census counts data (23 species, ~46,000 specimens). SSTs show that MIS 12 was the longest, sustained cold period, while the coldest temperature was recorded in MIS 5d (~8º C). Interglacials MIS 11 and 5e are the two warmest stages of the record, with SSTs reaching ~18.5º C, about ~2º C warmer than present day. We find that contrary to either the western Tasman Sea or offshore eastern New Zealand, the eastern Tasman Sea has been fairly isolated from any major influx of subpolar or subtropical species carried in with surface water from either high or low latitude sources. Subtropical taxa abundance (Globigerinoides ruber, Neogloboquadrina dutertrei (D), Globigerinoides sacculifer, Globigerinella aequilateralis, Sphaeroidinellopsis dehiscens, Truncorotalia truncatulinoides (D), Beella digitata) is low (average ~0.6%) and only prominent during peak interglacials. Subantarctic taxa abundance (Neogloboquadrina pachyderma, Neogloboquadrina dutertrei (S)) is low (average ~5.1%), but significant, particularly in glacial periods. Comparison of faunal and SSTANN data along with ratios of Nq. pachyderma:Nq. incompta (previously referred to as coiling ratios of Nq. pachyderma) and absolute abundance of planktic productivity (a productivity proxy) suggest that the STF migrated northwards towards the site in all glacial periods, and may have moved over the site in MIS 12 and possibly MIS 5d. A latitudinal SSTANN 25 comparison between offshore eastern and western New Zealand reveals that MD06-2986 (~43º S) is most similar (~0.5º C) to ODP Site 1125 (~42º S). On the contrary, ODP Site 1119 (44º S) is ~5º C cooler than MD06-2986. This comparison highlights the significant changes in surface water masses off eastern New Zealand that exist in such a short span of latitude because of the influence of a complex submarine topography.</p>

Pliocene evolution of the tropical Atlantic thermocline depth

It has been hypothesized that global temperature trends are tightly linked to tropical thermocline depth, and that thermocline shoaling played a crucial role in the intensification of late Pliocene northern hemisphere glaciation. The Pliocene thermocline evolution in the Pacific Ocean is well documented and supports this hypothesis, but thermocline records from the tropical Atlantic Ocean are limited. We present new planktonic foraminiferal Mg/Ca, δ18O and δ13C records from the late Pliocene interval at Ocean Drilling Program Site 959 in the eastern equatorial Atlantic (EEA), which we use to reconstruct ocean temperatures and relative changes in salinity and thermocline depth. Data were generated using surface-dwelling Globigerinoides ruber and subsurface-dwelling Neogloboquadrina dutertrei. Reduced gradients between the surface and subsurface records indicate deepening of the EEA thermocline at the end of the Mid-Piacenzian Warm Period (mPWP; ~3.3–3.0 Ma). We connect our late Pliocene records to previously published early Pliocene δ18O data from Site 959 and compare these to the Site 1000 in the Caribbean Sea. Over the course of the Pliocene, thermocline changes in the EEA and Caribbean Sea follow similar patterns, with prominent step-wise thermocline deepening between ~5.5 and 4.0 Ma, gradual shoaling up to the mPWP, followed by minor deepening at the end of the mPWP. The tropical thermocline depth evolution of the tropical Atlantic differs from the Pacific, which is characterized by gradual basin-wide shoaling across the Pliocene. These results potentially challenge the hypothesized link between tropical thermocline depth and global climate. The mechanisms behind the periodically divergent Pacific and Atlantic thermocline movements remain speculative. We suggest that they are related to basin geometry and heterogenous temperature evolutions in regions from where thermocline waters are sourced. A positive feedback loop between source region temperature and tropical cyclone activity may have amplified tropical thermocline adjustments.

Foraminifera biostratigraphy and paleoenvironmental studies of well-x, eastern Niger delta

Ditch cutting samples from Well-X drilled in the Eastern part of the Niger delta were subjected to biostratigraphy and paleoenvironmental studies using micropaleontological analysis to identify the foraminifera present in the sections penetrated by the well.A total of 50 (fifty) foraminifera species made up of benthonic and planktic spp were recovered from the sections. The marker species identified are Globorotalia acostaensis, Globorotalia mernadii cultrate, Neogloboquadrina dutertrei, Globorotalia plesiotumida, Globorotalia obesa, Globorotalia nepenthes, Sphaeroidinella subdehiscens, Neogloboquadrina dutertrei, Globigerinoides sudquadratus.The four (4) biozones identified are N16 (Late Miocene 9.5Ma - 10.9Ma), N15-N14, N13-N12 and N12-N11 (Middle Miocene with corresponding ages 10.9Ma -11.8Ma, 11.8Ma-12.2Ma and 12.2Ma respectively).Using the encountered benthonic foraminiferal species, the paleoecology was determined; and it was revealed that the paleoenvironment of the section ranges from Inner Neritic to Outer Neritic Environment. Also, the lithological analysis revealed an intercalation of Shale, Mudstone and Sand which indicates various paleoecological episodes that led to their deposition.The age of the well was inferred from the bioevents of the marker species to be Middle Miocene to Late Miocene with the sparse occurrence of the Calcareous Benthic and the Plankonic species suggesting a shallow marine environment.

CHANGES OF THERMOCLINE DEPTH AT THE SUMBA ISLAND OFFSHORE BASED ON PLANKTONIC FORAMINIFERAL ASSEMBLAGES AND ITS IMPLICATION TO EUTROPHICATION SINCE THE LAST DEGLACIATION (~18 ka BP): A PRELIMINARY STUDY

Changes of the thermocline depth (DOT) at the Sumba Island offshore are not well-known compared to the DOT changes in the Timor Sea, the main exit passage of the Indonesian Through-flow (ITF). Planktonic foraminiferal assemblages in cores collected from the southwest Sumba offshore (ST08) and Sumba Strait (ST12, ST13, and ST14) were used as a tool to infer the DOT and paleoproductivity changes at the Sumba Island offshore. The DOT changes were indicated from the thermocline and mixed layer dwellers’ relative abundance while the paleoproductivity changes were indicated from the relative abundance of Neogloboquadrina dutertrei. This study suggests a contrast between the DOT pattern at the Sumba Island offshore and the DOT pattern in the Timor Sea during the Last Deglaciation–Holocene. The contrast DOT pattern indicated that the multi-millennial changes of the Australian-Indonesian monsoon (AIM) during the Last Deglaciation– Holocene were the main factors behind the DOT changes in this region while the effects of El Niño Southern Oscillation (ENSO) –like, Indian Ocean Dipole (IOD) –like, and ITF to DOT changes were minimal. Paleoproductivity enhancement at the Sumba Island offshore was not solely related to the monsoon-driven coastal upwelling intensification, which resulted in the DOT shoaling and eutrophic condition. The increase of nutrient availability in surface water due to river runoff increase and changes in the lifted water mass nature were also able to enhance productivity in this region.

Seawater pH reconstruction using boron isotopes in multiple planktonic foraminifera species with different depth habitats and their potential to constrain pH and <i>p</i>CO₂ gradients

Boron isotope systematics of planktonic foraminifera from core-top sediments and culture experiments have been studied to investigate the sensitivity of δ11B of calcite tests to seawater pH. However, our knowledge of the relationship between δ11B and pH remains incomplete for many taxa. Thus, to expand the potential scope of application of this proxy, we report δ11B data for seven different species of planktonic foraminifera from sediment core tops. We utilize a method for the measurement of small samples of foraminifera and calculate the δ11B-calcite sensitivity to pH for Globigerinoides ruber, Trilobus sacculifer (sacc or without sacc), Orbulina universa, Pulleniatina obliquiloculata, Neogloboquadrina dutertrei, Globorotalia menardii, and Globorotalia tumida, including for unstudied core tops and species. These taxa have diverse ecological preferences and are from sites that span a range of oceanographic regimes, including some that are in regions of air–sea equilibrium and others that are out of equilibrium with the atmosphere. The sensitivity of δ11Bcarbonate to δ11Bborate (e.g., Δδ11Bcarbonate∕Δδ11Bborate) in core tops is consistent with previous studies for T. sacculifer and G. ruber and close to unity for N. dutertrei, O. universa, and combined deep-dwelling species. Deep-dwelling species closely follow the core-top calibration for O. universa, which is attributed to respiration-driven microenvironments likely caused by light limitation and/or symbiont–host interactions. Our data support the premise that utilizing boron isotope measurements of multiple species within a sediment core can be utilized to constrain vertical profiles of pH and pCO2 at sites spanning different oceanic regimes, thereby constraining changes in vertical pH gradients and yielding insights into the past behavior of the oceanic carbon pumps.

Deglacial 14C reservoir ages of surface waters at the northern boundary of Peruvian coastal upwelling

&lt;p&gt;To constrain the accurate age of a marine sediment record, the radiocarbon (&lt;sup&gt;14&lt;/sup&gt;C) ages need to be corrected for short-term and small-scale changes in planktic &lt;sup&gt;14&lt;/sup&gt;C reservoir ages (R&lt;sub&gt;plank&lt;/sub&gt;). Nevertheless, accurate records of past changes in R&lt;sub&gt;plank&lt;/sub&gt; are scarce. Here we present a high-resolution record of deglacial &lt;sup&gt;14&lt;/sup&gt;C ages measured on &lt;em&gt;Globigerina bulloides&lt;/em&gt; in sediment core M77/2-59-1 from the northern boundary (~4&amp;#176;S, 997 m) of the Peruvian upwelling zone. The fine structure of jumps and plateau boundaries in the &lt;sup&gt;14&lt;/sup&gt;C record were tuned to synchronous, thus global structures in the atmospheric &lt;sup&gt;14&lt;/sup&gt;C record of Lake Suigetsu (Bronk Ramsey et al., 2012) and used as tie points for an age model with semi-millennial resolution, moreover to reconstruct deglacial changes in R&lt;sub&gt;plank &lt;/sub&gt;from 17 to 11 cal. ka. In our record, R&lt;sub&gt;plank&lt;/sub&gt; drops from 1250 &lt;sup&gt;14&lt;/sup&gt;C yr prior to 14 cal. ka to ~600 &amp;#8211; 450 &lt;sup&gt;14&lt;/sup&gt;C yr until the plateau named Top of Younger Dryas. The drop suggests a major decrease in coastal upwelling, possibly the result of a southward (poleward) expansion of the Intertropical Convergence Zone and related shift in the southeastern trade wind belt during the B&amp;#248;lling-Aller&amp;#248;d. Subsequent to 14 cal. ka our R&lt;sub&gt;plank &lt;/sub&gt;values are roughly similar to values obtained for thermocline waters near the equator from the age difference between &lt;sup&gt;14&lt;/sup&gt;C ages of wood chunks and &lt;sup&gt;14&lt;/sup&gt;C of &lt;em&gt;G. ruber&lt;/em&gt; (Zhao &amp; Keigwin, 2018). Prior to 14 cal. ka our R&lt;sub&gt;plank &lt;/sub&gt;are ~800 &lt;sup&gt;14&lt;/sup&gt;C yr higher, which corroborates the presumed latitudinal shift of coastal upwelling. Our &lt;sup&gt;14&lt;/sup&gt;C ages measured on G. bulloides differ in part from paired &lt;sup&gt;14&lt;/sup&gt;C ages of &lt;em&gt;Neogloboquadrina dutertrei&lt;/em&gt;, indicating their habitat in different water masses prior to 14 cal. ka, in support of the upwelling affinity of &lt;em&gt;G. bulloides&lt;/em&gt;. In addition, we used our R&lt;sub&gt;plank&lt;/sub&gt; values to accurately derive past ventilation ages of intermediate waters near 1000 m depth based on the difference of paired benthic and planktic &lt;sup&gt;14&lt;/sup&gt;C ages, which is important to constrain centennial to millennial scale changes in circulation influencing the extent of the Peruvian oxygen minimum zone.&lt;/p&gt;&lt;p&gt;References:&lt;/p&gt;&lt;p&gt;Bronk Ramsey, C., et al., Science, 338, 370&amp;#8211;374, 2012.&lt;/p&gt;&lt;p&gt;Zhao &amp; Keigwin, Nature communications, 9, 3077, 2018.&lt;/p&gt;

Reliability of foraminiferal Na/Ca as a direct paleo-salinity proxy in various planktonic species from the eastern tropical North Atlantic

&lt;p&gt;&lt;span&gt;Foraminiferal Na/Ca in planktonic and benthic foraminifers is a promising new method to assess directly past seawater salinities, which complements existing approaches (e.g., paired shell Mg/Ca and &amp;#948;&lt;/span&gt;&lt;sup&gt;&lt;span&gt;18&lt;/span&gt;&lt;/sup&gt;&lt;span&gt;O, shell Ba/Ca). Recent culture and field calibration studies have shown a significant positive relationship of Na incorporation into foraminiferal calcite shells with increasing salinity [1, 2], as confirmed by our culture study of &lt;em&gt;Trilobatus sacculifer&amp;#160;&lt;/em&gt;[3]. However, we note that the sensitivity of Na/Ca in response to salinity changes is species-specific and regional dependent, whereas temperature could be excluded as a secondary influencing factor [2, 3, 5]. Na/Ca values vary from 1&amp;#8211;3 mmol/mol for the same salinity within and between foraminiferal species, suggesting a dominant biological control.&amp;#160;&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;To further evaluate the robustness of Na/Ca for its application as a reliable proxy, we here examine possible secondary controls on foraminiferal Na/Ca with new data for commonly used species for paleoreconstructions (&lt;em&gt;Globigerinoides elongatus&lt;/em&gt;,&amp;#160;&lt;em&gt;G. ruber&amp;#160;&lt;/em&gt;(pink), &lt;em&gt;Orbulina universa&lt;/em&gt;, &lt;em&gt;Globigerina bulloides&lt;/em&gt;, &lt;em&gt;Neogloboquadrina dutertrei&lt;/em&gt;) collected by plankton tows in the eastern tropical North Atlantic during R/V Meteor cruise M140. We performed laser ablation ICP-MS measurements on single foraminiferal shells from depth-resolved plankton tows in 20 m net-intervals from locations where salinity was essentially constant, &lt;/span&gt;while seawater &lt;span&gt;pH and total alkalinity differed&lt;/span&gt;&amp;#160;by ~0.5 and 100 &amp;#181;mol/kg, respectively. Plankton tow samples&amp;#160;&lt;span&gt;provide new insights &lt;/span&gt;in&lt;span&gt;to &lt;/span&gt;the &lt;span&gt;possible effects of &lt;/span&gt;natural variations in &lt;span&gt;carbonate system parameters on Na incorporation into calcite tests with increasing water depth. The comparison of living foraminifers to sedimentary shells gives further information about the preservation state of Na/Ca in calcite shells over time, whereas fossil shells have mostly undergone gametogenesis during their life-time, or were affected post mortem by early diagenesis (sedimentation) processes. Those foraminifers were collected from surface sediments (M65-1) located in proximity to plankton tows. Our results show that all measured species, either from plankton tows or buried in the sediment, are within the Na/Ca range of previous studies [1-5], which increases the confidence for a robust Na/Ca to salinity proxy. However, the offset of ~2-5 mmol/mol between living foraminifers collected in surface waters (0-20 m) and fossil assemblages of the same species could be related to spine loss at the end of a foraminiferal life cycle [4]. In addition, the usage of inconsistent test sizes could further influence the foraminiferal Na/Ca signal. Our results reveal significant (R = &lt;/span&gt;&lt;span&gt;-&lt;/span&gt;&lt;span&gt;0.97, &lt;em&gt;p&lt;/em&gt;&lt;0.03&lt;/span&gt;&lt;span&gt;) decreasing Na/Ca values with increasing test sizes between &lt;/span&gt;&lt;span&gt;180-250 &amp;#181;m &lt;/span&gt;&lt;span&gt;for&amp;#160;&lt;em&gt;G. ruber&amp;#160;&lt;/em&gt;(pink, white), &lt;em&gt;N. dutertei&amp;#160;&lt;/em&gt;and&amp;#160;&lt;em&gt;T. sacculifer&lt;/em&gt;, whereas values increase again with larger size classes &gt;355 &amp;#181;m (R = 0.87, &lt;em&gt;p&lt;/em&gt;&lt;0.02).&lt;/span&gt;&lt;span&gt;&amp;#160;&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;[1] Wit et al. (2013) Biogeosciences &lt;strong&gt;10&lt;/strong&gt;, 6375-6387. [2] Mezger et al. (2016) Paleoceanography &lt;strong&gt;31&lt;/strong&gt;, 1562-1582. [3] Bertlich et al. (2018) Biogeosciences &lt;/span&gt;&lt;strong&gt;15&lt;/strong&gt;, 5991&amp;#8211;6018.&lt;span&gt;[4] Mezger et al. (2019) Biogeosciences &lt;strong&gt;16&lt;/strong&gt;, 1147-1165, 2019. [5] Allen et al. (2016) Geochim. Cosmochim. Acta &lt;strong&gt;193&lt;/strong&gt;, 197-221.&lt;/span&gt;&lt;/p&gt;

Inconsistent change in surface hydrography of the eastern Arabian Sea during the last four glacial–interglacial intervals

The eastern Arabian Sea is influenced by both the advection of upwelled water from the western Arabian Sea and winter convective mixing. Therefore, sediments collected from the eastern Arabian Sea can help to understand the long-term seasonal hydrographic changes. We used the planktonic foraminifera census and stable isotopic ratio (δ18O) from sediments drilled during the International Ocean Discovery Program Expedition 355 to reconstruct surface hydrographic changes in the eastern Arabian Sea during the last 350 kyr. The increased abundance of Globigerina bulloides suggests enhanced advection of upwelled water during the latter half of MIS7 and the beginning of MIS6, as a result of a strengthened summer monsoon. A large drop in upwelling and/or advection of upwelled water from the western Arabian Sea is inferred during the subsequent interval of MIS6, based on the rare presence of G. bulloides. The comparable relative abundance of Neogloboquadrina dutertrei, G. bulloides and Globigerinoides ruber suggests that during the early part of MIS5, hydrographic conditions were similar to today. The upwelling decreased and winter convection increased with the progress of the glacial interval. A good coherence between planktonic foraminiferal assemblage-based monsoon stacks from both the eastern and western Arabian Sea suggests a coeval response of the entire northern Arabian Sea to the glacial–interglacial changes. The glacial–interglacial difference in δ18Osw-ivc was at a maximum with 4–5 psu change in salinity during Termination 2 and 3, and a minimum during Termination 4. The significantly reduced regional contribution to the glacial–interglacial change in δ18Osw-ivc during Termination 4 suggests a lesser change in the monsoon.