Cold-water Taxa Research Articles

Changes in chironomid communities during the Holocene in Lake Polevskoye (Zaonezhsky Peninsula, northwestern Russia)

We reconstructed paleoclimatic and paleoenvironmental changes based on the analyses of sediments from the Lake Polevskoye on the Zaonezhsky Peninsula in northwestern Russia. The change in the taxonomic composition of chironomids was analysed in the studied core. The age of the sediments covers ca 7.1 thousand years. Based on the cluster analysis, 3 main stratigraphic zones were identified. From 7.1 to 5.2 ka cal. yrs. BP, phytophilic taxa associated with shallow lakes dominated. Later between 5.2 – 2.0 ka cal. yrs. BP chironomids biodiversity increased. During this period, cold-water taxa appeared, which might indicate some cooling during this period. There was also a simultaneous increased in the number of profundal and semi-terrestrial species, which may indicate the changes of the water level in the lake and paludification. After 2.0 ka cal. yrs. BP the total number of species decreased. The dominant taxa associated with shallow water levels and moderately warm climatic conditions. Changes in the taxonomic composition of chironomids in Lake Polevskoye responded to paleoenvironmental changes. During the studied period, there was an increase in diversity of chironomids and a change in dominant taxa. The reconstructed conditions showed an increase in the water level in the lake from 5.2 to 2.0 ka cal. yrs. BP, as well as a gradual increase in trophicity.

Metabarcoding Extends the Distribution of Porphyra corallicola (Bangiales) into the Arctic While Revealing Novel Species and Patterns for Conchocelis Stages in the Canadian Flora

Porphyra corallicola was described based on a filamentous red alga inadvertently introduced into culture from a crustose coralline alga. This species is known only in its sporophyte (Conchocelis) stage, being possibly asexual and lacking the charismatic and “collectable” gametophyte stage. Consequently, little is known of its range and distribution. Taxon-targeted metabarcoding was explored as a pathway to gain insights into the vertical (intertidal versus subtidal) and biogeographical distribution of this species, as well as to assess host diversity. We also wanted to ascertain if other species occur in only the Conchocelis stage in the Canadian flora. Primers targeting a short (521 bp) region of the plastid rbcL gene in the Bangiales were used to screen DNA from 285 coralline crusts collected throughout Canada and adjacent waters. In addition to confirming the presence of P. corallicola in the Bay of Fundy, this species was recovered from coralline crusts along the coast of Nova Scotia (n = 1) and in the low Arctic (Labrador; n = 2), greatly extending its range and suggesting it is a cold-water taxon. We have confirmed its presence in both the low intertidal and subtidal (to 10 m), and its occurrence in three different coralline species, suggesting that it lacks host specificity. In total, nine genetic groups of Bangiales were uncovered in our survey, six matching entries currently in GenBank and three apparently novel genetic groups—two from the northeast Pacific and one from the low Arctic. Notable host and ecological patterns are discussed. This method, when further developed, will facilitate the study of Conchocelis stages in nature, which will greatly enhance ecological knowledge of bangialean species.

Paleoenvironmental and paleoclimatic changes during the Late Cretaceous and Cretaceous–Paleogene (K/Pg) boundary transition in Tattofte, External Rif, northwestern Morocco: implications from dinoflagellate cysts and palynofacies

This paper presents a quantitative study of dinoflagellate cysts (dinocysts) and palynofacies of the Campanian–Danian marly succession at the village of Tattofte (western External Rif, northwestern Morocco). The paleoenvironmental and paleoclimatic interpretations, inferred from this palynologic analysis, are compared to coeval sequences of other areas in the Northern Hemisphere. Changes in the relative abundances of dinocyst taxa, which are paleoenvironmental indicators, throughout the section suggest a deposition in a marine inner to outer neritic setting. The upper Campanian dinocyst assemblage is characterized by the presence of outer neritic-oceanic and low productivity indicator taxa (e.g., Spiniferites spp., Odontochitina spp.) and cold-water taxa (e.g., Manumiella spp., Chantangiella spp., Laciniadinium spp.), whereas, the lower Maastrichtian assemblage is characterized by inner neritic, high productivity and warm-water indicator taxa (e.g., Palaeocystodinium spp., Andalusiella spp.). The upper Maastrichtian dinocyst assemblage displays a return to an outer neritic environment under a transgressive regime, but with a cooling pulse and a moderate productivity. However, the Cretaceous–Paleogene (K/Pg) boundary interval records remarkable changes in the relative abundances of dinocyst taxa, indicating an inner neritic (coastal) setting, which is the most proximal in the study section; such changes reflect instable paleoenvironmental conditions which may be related to global cooling periods, likely caused by the Deccan volcanism in India and/or the Chicxulub asteroid impact in Mexico at the K/Pg boundary. In the Danian, the dinocyst relative abundances indicate a gradual return to stable environmental conditions.A quantitative analysis of the kerogen plots (palynomorphs, phytoclasts and amorphous organic matter (AOM)) reveals five types of palynofacies, generally indicating oxic to suboxic marine environments. The upper Campanian and upper Maastrichtian (lowermost part) strata are characterized by a playnofacies (V), indicating a distal shelf, while the lower Maastrichtian and lower Danian (uppermost part) strata record a playnofacies (III), reflecting an intermediate inner-outer neritic environment. However, the K/Pg boundary transition is characterized by playnofacies types (I) and (II), indicating a proximal (coastal) environment.

Calcareous nannofossil biostratigraphy of the Lower\u2013Middle Pleistocene boundary of the GSSP, Chiba composite section in the Kokumoto Formation, Kazusa Group, central Japan, and implications for sea-surface environmental changes

The Chiba composite section (CbCS), in the middle of the Boso Peninsula in central Japan, was ratified as the Global Boundary Stratotype Section and Point (GSSP) for the Lower–Middle Pleistocene boundary, accompanied by the Matuyama–Brunhes (M–B) paleomagnetic polarity boundary in January 2020. This study examined the calcareous nannofossil biostratigraphy of the CbCS to describe potential nannofossil events and discuss sea-surface environments around the M–B paleomagnetic polarity boundary. There are no clear biohorizons at the M–B paleomagnetic polarity boundary, although a temporary disappearance of Gephyrocapsa specimens (≥ 5 μm in diameter), an important calcareous nannofossil genus in the Pleistocene, occurs just above the Lower–Middle Pleistocene boundary. Although this is a characteristic event around the M–B paleomagnetic polarity boundary, it is unclear whether the event is globally traceable.Changes in the environmental proxy taxa of calcareous nannofossils in the CbCS revealed that sea-surface environments were driven by glacial-interglacial and millennial-scale climate forces. The time-transgressive change of the Tn value, a calcareous nannofossil temperature index, is mostly concordant with the planktonic foraminiferal oxygen isotope fluctuation. Abundant occurrences of a warm-water species, Umbilicosphaera spp., indicate that the Kuroshio Current was strong after ~ 783 ka. Even the strong influence of the Kuroshio Current, cooling events related to southward movements of the Kuroshio Front occurred every 10,000 years based on the presence of a cold-water taxon, Coccolithus pelagicus. Additionally, the inflow of coastal waters strengthened after ~ 778 ka because of abundant occurrences of Helicosphaera spp. Millennial-scale sea-surface changes were also inferred from detected floral fluctuations of less than 10,000 years.Graphical abstract

Biostratigraphy and paleoecologic inferences during the late Campanian–Maastrichtian interval: Evidence based on calcareous nannofossils from Goban Spur

Abstract This paper presents a biostratigraphic revision and a quantitative study of the calcareous nannofossils from DSDP Leg 80 – Hole 550B. A total of 42 samples were analyzed, revealing 78 species whose preservation varied from slightly to moderately dissolved with slight to severe overgrowth. Biostratigraphy indicates deposition during the late Campanian to late Maastrichtian, incorporating zones UC15d to UC20b. The quantitative nannofossil data recovered shows that Watznaueria barnesiae and Micula staurophora dominate the assemblages, which can be attributed to a low preservation potential for the depositional environment. Cold-water taxa ( Kamptnerius magnificus , Ahmuellerella octoradiata, and Arkhangelskiella cymbiformis ) are present in very low percentages, with their maximum values occurring inside the UC17 biozone.

Seasonality fluctuations recorded in fossil bivalves during the early Pleistocene: Implications for climate change

Understanding the transformations of the climate system may help to predict and reduce the effects of global climate change. The geological record provides a unique archive that documents the long-term fluctuations of environmental variables, such as seasonal change. Here, we investigate how seasonal variation in seawater temperatures varied in the Mediterranean Sea during the early Pleistocene, approaching the Early-Middle Pleistocene Transition (EMPT) and the beginning of precession-driven Quaternary-style glacial–interglacial cycles. We performed whole-shell and sclerochemical stable isotope analyses (δ18O, δ13C) on bivalves, collected from the lower Pleistocene Arda River marine succession (northern Italy), after checking shell preservation. Our results indicate that seawater temperature seasonality was the main variable of climate change in the Mediterranean area during the early Pleistocene, with the Northern Hemisphere Glaciation (NHG) exerting a control on the Mediterranean climate. We show that strong seasonality (14.4–16.0°C range) and low winter paleotemperatures (0.8–1.6°C) were likely the triggers leading to the establishment of widespread populations of so called “northern guests” (i.e., cold water taxa) in the Mediterranean Sea around 1.80Ma. The shells postdating the arrival of the “northern guests” record a return to lower seasonal variations and higher seawater paleotemperatures, with seasonality increasing again approaching the EMPT; the latter, however, is not associated with a corresponding cooling of mean seawater paleotemperatures, showing that the observed seasonality variation represents a clear signal of progressive climate change in the Mediterranean Sea.

Calcareous nannoplankton assemblage changes linked to paleoenvironmental deterioration and recovery across the Cretaceous–Paleogene boundary in the Betic Cordillera (Agost, Spain)

Investigations of calcareous nannoplankton assemblages including species richness and abundance data were performed across the K–Pg boundary interval at Agost (SE Spain), between −100cm and +100cm, below and, respectively, above the boundary, at a considerable high resolution averaging 2cm. From a total of 98 species of the Upper Maastrichtian, only 13 survived mass extinction, while the rest of the 86% vanished in the K–Pg fallout layer. A slight progressive decline in species richness and abundance was observed toward the top of the Maastrichtian, where mixed assemblages, consisting of both cold-water taxa and typical Tethyan ones are present. Four successive acme events were observed, i.e. Markalius inversus and the calcareous dinoflagellate genus Thoracosphaera starting from the base of the Paleocene, followed by those of Braarudosphaera bigelowii and Neobiscutum parvulum. The most prominent acme intervals belong to Thoracosphaera spp. and B. bigelowii, opportunistic taxa, for which the survival strategy may be linked to their capability to encyst and survive severe environmental deterioration. At the upper part of the studied succession, calcareous nannoplankton assemblages are already dominated by survivor species, as well as incoming ones, showing an early pioneer calcareous nannoplankton ecosystems about 35–40kyr after the K–Pg boundary. Correlation between the calcareous nannoplankton assemblage fluctuation, including species richness and abundance, and the paleoenvironmental changes, such as the eustatic and climatic modifications, are also discussed.

Diatom records in the Quaternary marine sequences around the Japanese Islands

Understanding the Quaternary is a key to estimating what the Earth's climate will be like in the future. Such studies demand high-resolution analyses based on paleoclimatic proxy records of changing Earth's orbital forcing and solar insolation that affect the climate system. Quaternary diatom biostratigraphy and paleoceanography have been well established based on the Quaternary marine sequences obtained by piston coring and deep-sea drilling around the Japanese Islands. This paper firstly reviews the Quaternary diatom datum levels that are directly tied to magnetic polarity, and then the late Pleistocene and Holocene rhythmic fluctuations in Td'-derived SSTs (°C) which correlate with the Earth's orbital parameters, and finally reveals the large and abrupt climatic changes that have occurred around the Japanese Islands on centennial to millennial time scales.The main aim is to provide the results of Td'-SSTs (°C) based on the late Pliocene to Pleistocene sequences from three holes obtained by deep-sea drilling (DSDP-ODP). The main difference between Td' and Twt is that Twt gives 0.5 values to Xt (warm transitional taxa). Thalassiosira oestrupii is grouped with Xt in Twt but with warm-water species in Td'. Differences between the Twt and Td'-SSTs (°C) curves at Hole 436 are unremarkable. The remarkable variations of paleo-temperatures based on Td'-SSTs (°C) show four conspicuous episodes which correspond to the double precession cycle of MIS 11. In the Japan Sea, the Twt ratio remarkably decreases at 2.6 Ma due to a large increase in cold-water taxa, and indicates the beginning of the glacial age defined as the Pliocene/Pleistocene boundary. Both Twt and Td'-SSTs (°C) increase at 2.60–2.0 Ma, and coincide with the lithologic change from diatom-bearing clay with few dark-colored layers to fine-grained sediments with distinct dark–light colored cycles. Wavelet analysis of Td'-SSTs (C) at Site 798 indicates a reversed saw-tooth pattern of 48 to 24-ky periods during 1.2–0.7 Ma, and 24 to 12-ky periods during 0.7–0 Ma, resulting in a change from longer to shorter cycles. These fluctuations correlate with the Earth's orbital parameters and climatic changes on a millennial time scale.

Brachiopods, fusulines and palynomorphs of the Mengkarang Formation (Early Permian, Sumatra) and their palaeobiogeographical significance

Brachiopods, fusulines and palynomorphs from the Lower Permian Mengkarang Formation (Sumatra, Indonesia) have been studied in order to establish the palaeogeographical position and the palaeolatitude of the West Sumatra Block. The position of the West Sumatra Block within the Palaeo-Tethys and Panthalassa oceans and its relationships to their marginal landmasses, in particular the Gondwana supercontinent and the Cathaysian palaeogeographical area, currently is uncertain.Brachiopods, fusulines and palynomorphs of the Lower Permian Mengkarang Formation were analysed to test the Gondwanan versus Cathaysian affinity of the West Sumatra Block. Six genera and two species of fossil brachiopods were identified: Neochonetes (Neochonetes) carboniferus (Keyserling, 1846), Marginifera (Arenaria) sp. ind., Reticulatia sp. ind., Stereochia aff. S. irianensisArchbold, 1981a, ?Protoanidanthus sp. ind., Cancrinella sp. ind., and an undetermined genus and species of the subfamily Toryniferinae. Multivariate analysis of the available brachiopod data including those from the Mengkarang Formation identified two groups, the first comprising Iran, Yukon, the Urals and West Sumatra, the second comprising South Thailand, Baoshan, central Afghanistan, Karakoram, India, West and East Australia, indicating that Lower Permian brachiopods from West Sumatra are best grouped with warm water taxa rather than with cold water taxa from the Gondwanan-Perigondwanan region.Six fusuline species belonging to five genera were identified from six limestone samples: Eostaffella sp., Schubertella sp., Pseudoschwagerina cf. afghanensisLeven, 1971, Pseudoschwagerina meranginensisThompson, 1936, Eoparafusulina ?haydeniLeven, 1971, Pseudofusulina rutschiThompson, 1936. The fusuline fauna is rather poor in terms of generic composition as it is composed mainly by widespread genera but, in a broad sense, the Lower Permian West Sumatra fauna is typical of palaeo-tropical Tethyan regions because of the common occurrence of large schwagerinids.Only one sample level in the Mengkarang Formation yielded abundant palynomorphs, dominated by Laevigatosporites spp. indeterminate bisaccate pollen, Florinites florini Imgrund, 1960 and Convolutispora sp. This assemblage is very different from coeval assemblages of the Gondwanan region, northern Palaeotethyan regions of Kazakhstan, and parts of western Europe and the Intrasudetic Basin, but has more affinity with the Cathaysian phytogeographic province as represented in northern China, Turkey and northern Iraq.

Further observations on the Jurassic dinoflagellate cyst Gonyaulacysta dentata (Raynaud 1978) Lentin & Vozzhennikova 1990 emended Riding 2012

Gonyaulacysta dentata is a large and morphologically distinctive dinoflagellate cyst. It is confined to the Late Callovian to earliest Oxfordian (Peltoceras athleta to Quenstedtoceras mariae zones) interval of the Boreal Realm and the Subboreal Province in the northern hemisphere, and has therefore been interpreted as a cold water species. The holotype of G. dentata is from the Staffin Shale Formation of Staffin Bay, Isle of Skye, northwest Scotland and has been lost. Consequently another well-preserved specimen from the Staffin Shale Formation of the Isle of Skye is proposed as a neotype. The ventral and apical areas of G. dentata are characterised by discontinuous, low, smooth sutural ridges. However, the 5″/6″, 4′/6″ and 4′/1′ sutures on the ventral side of the epicyst are frequently indicated by relatively high denticulate crests. The 2″′/1p suture and the cingular sutures may also be developed on the ventral face. Conversely, the dorsal and lateral sutural crests, except in the apical area, are prominent and denticulate. G. dentata is present in East Greenland. Two specimens were recorded, as Gonyaulacysta eisenackii subsp. oligodentata, from the Late Callovian of Jameson Land. These are probably from the Olympen Formation, and not the Upper Vardekløft Formation as was originally stated. This occurrence is entirely consistent with the Boreal distribution of G. dentata. The range of G. dentata, the Callovian–Oxfordian transition, was characterised by significantly lowered palaeotemperatures. Several other dinoflagellate cyst species are also believed to be cold water taxa, and migrated south from the Boreal Realm into Europe at this time.

A high resolution multi-proxy record of pronounced recent environmental change at Baker Lake, Nunavut

Arctic aquatic systems are considered to be especially sensitive to anthropogenic disturbance, which can have cascading effects on biological communities as aquatic food-web structure is altered. Bio-indicators that respond to major limnological changes can be used to detect and infer major environmental change, such as climate warming, with the use of paleolimnological techniques. A multi-proxy approach was used to quantify recent environmental changes at Baker Lake, Nunavut, Arctic Canada. Analyses of fossilized remains of chironomids and diatoms were conducted on a sediment core of 20 cm in length sampled at 0.5-cm intervals. A new surface sediment training set of subfossil chironomid assemblages from 65 lakes across the eastern Canadian Arctic generated a robust (r jack 2 = 0.79) surface water paleotemperature transfer function. The transfer function was applied to stratigraphic intervals from the Baker Lake sediment core to generate a paleotemperature reconstruction of sub-decadal resolution. The surface water temperature reconstruction inferred a 2°C increase in mid-summer surface water temperature for Baker Lake over the last 60 years, which was corroborated by the local instrumental record spanning the period of 1950–2007 AD. The chironomid record shows a recent decline of several cold-water taxa and appearance of warm-water indicators. This shift in community structure began circa 1906 AD, and intensified after 1940 AD. The corresponding fossil diatom record showed an increase in small planktonic Cyclotella taxa over the past 60 years, intensifying in the last 5 years, which also suggests a warmer climate and longer ice-free periods. The shifts in the diatom assemblages began later than the shifts in the chironomid assemblages, and were of lower magnitude, reflecting differences in the mechanisms in which these two indicators respond to environmental change.

The Jurassic dinoflagellate cyst Gonyaulacysta dentata (Raynaud 1978) Lentin & Vozzhennikova 1990 emend. nov.: An index species for the Late Callovian to earliest Oxfordian of the northern hemisphere

Gonyaulacysta dentata is a very large and morphologically distinctive dinoflagellate cyst species which was first described from the Callovian (Middle Jurassic) strata of the Isle of Skye, northwest Scotland. The diagnosis and description of this species are emended herein in order to document the characteristic elongate pentagonal outline, the apicular structure, the bicavate cyst organisation, the prominent dorsal and lateral sutural crests which are typically denticulate, the discontinuous, low-relief midventral sutural ridges and the lack of a periarchaeopyle. Gonyaulacysta dentata is a reliable index taxon for the Late Callovian to earliest Oxfordian (Peltoceras athleta to Quenstedtoceras mariae zones) of the Boreal Realm and the Subboreal Province in the northern hemisphere. It is especially prominent in the Boreal Realm and the northern part of the Subboreal Province, and has been recorded from the Barents Sea region, arctic Canada, offshore Norway, the central and northern North Sea and northern Scotland. Typically this species represents a relatively low proportion of the overall dinoflagellate cyst assemblages. There are also reports of very rare specimens of Gonyaulacysta dentata from further south in the Northwest European Subprovince, i.e. France, Germany and Poland. It therefore appears to be a characteristic Boreal taxon, but low numbers migrated southwards into the Northwest European Subprovince due to a fall in palaeotemperatures during the Callovian-Oxfordian transition. The southwards expansion of this short-lived species parallels the southward migration of the Boreal ammonite family Cardioceratidae. There is a virtually mutually exclusive relationship between the Arctic species Gonyaulacysta dentata and the apparently warm-loving taxon Scriniodinium crystallinum during the Late Callovian to Early Oxfordian interval. This is consistent with the interpretation of Gonyaulacysta dentata as a cold water taxon.

Zooplankton species composition is linked to ocean transport in the Northern California Current

In the Northern California Current (NCC), zooplankton communities show interannual and multiyear shifts in species dominance that are tracked by survival of salmon populations. These zooplankton community changes correlate with the Pacific Decadal Oscillation (PDO) index: a 'warm-water' copepod species group is more abundant during warm (positive) phases of the PDO and less abundant during cold (negative) phases; the reverse occurs for a 'cold-water' species group. The observed relationship led to the hypothesis that the relative dominance of warm/cold-water copepods in the NCC is driven by changes in the horizontal advection of surface water over different phases of the PDO. To test this hypothesis, variation in surface water advection to coastal regions of the NCC over the period of 1950-2008 was investigated using a Regional Ocean Modeling System (ROMS) and passive tracer experiments, then was compared with zooplankton collected off Oregon since 1996. Results showed that surface water advection varied with the phase of the PDO; the low-frequency component of advection anomalies strongly correlated with copepod species composition (R > 0.9). During positive phases of the PDO, current anomalies were northward and onshore, resulting in transport of warmer waters and the associated copepods into the region. During negatives phases, increased equatorward current anomalies led to a copepod community that was dominated by cold-water taxa. Our results support the hypothesis that climate-driven changes in basin-scale circulation controls copepod community composition in the NCC, and demonstrate that large-scale climate forcings downscale to influence local and regional ecosystem structure.

Use of thermal preference metrics to examine state biomonitoring data for climate change effects

Analyses of long-term data are an important component of climate-change research because they can help further our understanding of the effects of climate change and can help establish expectations for biological responses to future climate changes. We used macroinvertebrate data to assess whether biological trends associated with directional climate change could be detected in routine biomonitoring data from Maine, North Carolina, and Utah. We analyzed data from 8 long-term biomonitoring sites that had 9 to 22 y of data, and focused on thermal-preference metrics based on cold- and warm-water-preference trait groups. The thermal-preference metrics were derived primarily from weighted-average or generalized-linear-model inferences based on data from each state database and are region specific. Long-term trends varied across sites and regions. At some sites, the thermal-preference metrics showed significant patterns that could be interpreted as being related to directional climate change, whereas at others, patterns were not as expected or were not evident. The strongest trends occurred at 2 Utah sites that had ≥14 y of data. At these sites, cold-water taxa were negatively correlated with air temperature, and, when years were grouped into hottest- and coldest-year samples, were strongly reduced in the hottest-year samples. Results suggest that thermal-preference metrics show promise for application in a biomonitoring context to differentiate climate-related responses from other stressors.

Hemipelagic cephalopods from the Maastrichtian (late Cretaceous) Parras Basin at La Parra, Coahuila, Mexico, and their implications for the correlation of the lower Difunta Group

Abstract Few biostratigraphic data exist from the Parras and La Popa basins, mainly due to the absence of index fossils. This paper describes 19 ammonoid species from 15 genera and 1 nautilid from La Parra, southeastern Coahuila, Mexico. The assemblage consists of Tethyan [(Baculites ovatus, Brahmaites (Anabrahmaites) vishnu, Fresvillia constricta, Hauericeras rembda, Pachydiscus (P.) ex gr. neubergicus, Solenoceras reesidei, Tetragonites cf. superstes], cosmopolitan (Anagaudryceras politissimum, Desmophyllites diphylloides, Diplomoceras cylindraceum, Gaudryceras kayei, Phyllopachyceras forbesianum, Pseudophyllites indra), and cold water taxa [Fresvillia teres, Hypophylloceras (Neophylloceras) surya, H. (N.) hetonaiense, Pachydiscus (P.) cf. egertoni]. Eutrephoceras sp. and Menuites juv. sp. were not determined to species level. A similar assemblage was recently described from the coeval Mendez Formation at Cerralvo, Nuevo Leon. Species endemic to North America, particularly the Western Interior Seaway, are absent at La Parra. The ammonoid assemblage and associated planktonic foraminifers allow for precise biostratigraphic assignation to the early Maastrichtian planktonic foraminiferal zone CF 5, and thus provide an important marker level for correlation of the lower Difunta Group. The new biostratigraphic data presented herein allow for the first time precise dating of the Canon del Tule Formation of the Difunta Group. Their combination with existing sequence- and magnetostratigraphic data improve the correlation of the lower Difunta Group with time-equivalent lithostratigraphic units such as the Cardenas Formation in Mexico. They also provide new insight into ammonoid migration patterns induced by sea-level changes. Baculites ovatus migrated into the La Popa Basin as a result of the sea-level highstand documented at La Parra.

Summer sea-surface temperatures and climate events on the North Icelandic shelf through the last 3000 years

Diatom data from core MD992271 on the North Icelandic shelf record a cooling trend through the last 3000 years. This is indicated by a general decrease in warm water species and an increase in cold water taxa. The relative abundance of these two diatom groups changed periodically, suggesting that the climate also fluctuated within this time period. The results of diatom-based transfer function calculation show that the summer sea-surface temperatures (SSTs) before 1400 cal. a BP were generally higher than the mean value for the last 3000 years and the summer SSTs fluctuated around the mean between 1400 and 700 cal. a BP, and dropped to the values below the mean after 700 cal. a BP. Four cooling events were distinguished, centered at around 2600, 1900, 1300 and 600 cal. a BP respectively. The results are not only consistent with the data from neighbouring cores HM107-03 and MD992275, but also comparable with those from the GISP2 ice core and from other marine sediment records in the North Atlantic. This suggests that changes in the summer SSTs reflect regional climate variations in the North Atlantic. On the North Icelandic shelf, the summer SST variation is a result of changes in the interaction between the cold and the warm currents in the area.

Late Pleistocene and Holocene palaeoenvironments in Golfo San Jorge, Patagonia: molluscan evidence

Palaeoenvironments suggested by molluscan assemblages preserved in Late Pleistocene and Holocene raised marine terraces along the Golfo San Jorge, central Patagonia coastline, Argentina, are reviewed in this work. A better precision of the stratigraphical and geographical ranges of the molluscs through their systematic review shows that all taxa have living representatives, mostly within the Argentine and/or Magellanean Zoogeographical Provinces. In general, no significant taxonomic appearances or disappearances are evident along this coastal area since the last Pleistocene highstand, reinforcing that the modern palaeoceanographical pattern, dominated by the cool Malvinas (Falkland) Current, has not been substantially modified and that the Magellanean Malacological Province has lasted at least since the Pleistocene (although with varying boundaries). The so-called marine terrace V, recently assigned to the Last Interglacial highstand (Oxygen Isotope Substage 5e?), showed in this area a molluscan assemblage characterised by very low diversity, dominantly large shells of Mulinia edulis and by cold-water taxa, in disagreement with higher sea surface temperatures within Oxygen Isotope Substage 5e (Last Interglacial Maximum) and suggesting softer substrates than in the modern adjacent littoral zone.

Late Holocene environmental changes inferred from diatoms in a lake on the western Taimyr Peninsula, northern Russia

Changes in the diatom assemblages preserved in a sediment core taken from a small lake located north of arctic treeline on the western Taimyr Peninsula, Russia, were examined in order to investigate late Holocene (i.e., ca 5000 cal yr BP to present) climatic and environmental changes within the region. Early diatom assemblages were dominated by benthic Fragilaria taxa and indicate a transitional phase in the lake history, most likely reflecting lake development and environmental change associated with treeline retreat to the south of the study site. Concurrent with pollen and macrofossil evidence of a vegetation shift to shrub tundra in the catchment basin at ca 4200 cal yr BP, an increase in cold-water taxa, followed by little change in diatom assemblages until ca 2800 cal yr BP, suggests that conditions were relatively cool and stable at this time. The last ∼2000 years of the Middendorf Lake record have been marked by fluctuating limnological conditions, characterized by striking successional shifts between Fragilaria pinnata and Aulacoseira distans var. humilis. Recent conditions in Middendorf Lake indicate an increase in diatom taxa previously rare in the record, possibly associated with twentieth-century climatic warming. The Middendorf Lake record indicates that significant limnological change may occur in the absence of catchment vegetation shifts, suggesting late-Holocene decoupling of aquatic and terrestrial responses to climatic and hydrological change. Our study results represent one of the few paleoecological records currently available from northern Russia, and highlight the need for further development of calibration data sets from this region.

SEASONAL DISTRIBUTION AND ABUNDANCE OF FISHES AND DECAPOD CRUSTACEANS IN A CAPE COD ESTUARY

Sampling in several habitat types (sand/mud, eelgrass, sand, gravel, macroalgae/mud) during all seasons with a variety of gears in Nauset Marsh, Massachusetts during 1985–1987 found a fauna consisting of 35 fish and 10 decapod crustacean species. Although most of the abundant species were found in several habitat types, species richness and habitat use appeared to be highest for vegetated habitats (eelgrass, macroalgae). The fishes and decapods were numerically dominated by cold-water taxa; however, numerous fish species, represented by rare individuals of predominantly southern forms, enriched the fauna. Species composition of Nauset Marsh could be distinguished from estuaries south of Cape Cod and even from the south shore of the cape. Both fishes and decapods were most abundant during the summer, apparently due to the contributions from spring and summer spawning in the estuary and the adjacent Atlantic Ocean. The location of Nauset Marsh and other estuaries on Cape Cod provide a unique opportunity to evaluate the importance of this region as a faunal boundary to estuarine species.

Late-Quaternary history of midge communities and climate from a tundra site near the lower Lena River, Northeast Siberia

Analysis of midge remains in late-Quaternary sediment, recovered from a lake situated north of treeline in northeast Siberia, indicates the occurrence of notable climatic fluctuations during the last 12 ka. The onset of late-glacial warming was disrupted by a marked cooling event – possibly correlative with the Younger Dryas – that occurred between 11,000 and 10,000 yr BP. Increases in the relative abundance of taxa typically found in tundra lakes, such as Hydrobaenus/Oliveridia and Parakiefferiella nigra, and the concurrent decrease in temperate taxa, such as Microtendipes and Corynocera ambigua, suggest climatic deterioration occurred during this interval. At approximately 10,000 yr BP there was a large increase in temperate taxa such as Microtendipes and C. ambigua, and a decline of essentially all cold-water taxa. This suggests that climate was warmer than present since the modern distribution of both Microtendipes and C. ambigua is limited to forested sites in this region. This warm interval lasted until approximately 6000 yr BP when there was a precipitous decline in temperate chironomid taxa and an increase in cold-water chironomid taxa, such as Paracladius, Hydrobaenus/Oliveridia, Abiskomyia, and Parakiefferiella nigra. This cooling continued through the late-Holocene and the modern tundra chironomid assemblage developed by approximately 1400 yr BP.