Diatom Abundance Research Articles

A 2-decade (1988–2009) record of diatom fluxes in the Mauritanian coastal upwelling: impact of low-frequency forcing and a two-step shift in the species composition

Abstract. Eastern boundary upwelling ecosystems (EBUEs) are among the most productive marine regions in the world's oceans. Understanding the degree of interannual to decadal variability in the Mauritania upwelling system is crucial for the prediction of future changes of primary productivity and carbon sequestration in the Canary Current EBUE as well as in similar environments. A multiyear sediment trap experiment was conducted at the mooring site CBmeso (“Cape Blanc mesotrophic”, ca. 20∘ N, ca. 20∘40′ W) in the highly productive coastal waters off Mauritania. Here, we present results on fluxes of diatoms and the species-specific composition of the assemblage for the time interval between March 1988 and June 2009. The temporal dynamics of diatom populations allows the proposal of three main intervals: (i) early 1988–late 1996, (ii) 1997–1999, and (iii) early 2002–mid 2009. The Atlantic Multidecadal Oscillation (AMO) appears to be an important driver of the long-term dynamics of diatom population. The long-term AMO-driven trend is interrupted by the occurrence of the strong 1997 El Niño–Southern Oscillation (ENSO). The extraordinary shift in the relative abundance of benthic diatoms in May 2002 suggests the strengthening of offshore advective transport within the uppermost layer of filament waters and in the subsurface and in deeper and bottom-near layers. It is hypothesized that the dominance of benthic diatoms was the response of the diatom community to the intensification of the slope and shelf poleward undercurrents. This dominance followed the intensification of the warm phase of AMO and the associated changes of the Atlantic Meridional Overturning Circulation. Transported valves (siliceous remains) from shallow Mauritanian coastal waters into the bathypelagic should be considered for the calculation and model experiments of bathy- and pelagic nutrients budgets (especially Si), the burial of diatoms, and the paleoenvironmental signal preserved in downcore sediments. Additionally, our 1988–2009 data set contributes to the characterization of the impact of low-frequency climate forcings in the northeastern Atlantic and will be especially helpful for establishing the scientific basis for forecasting and modeling future states of the Canary Current EBUE and its decadal changes.

Iron metabolism strategies in diatoms.

Diatoms are one of the most successful group of photosynthetic eukaryotes in the contemporary ocean. They are ubiquitously distributed and are the most abundant primary producers in polar waters. Equally remarkable is their ability to tolerate iron deprivation and respond to periodic iron fertilization. Despite their relatively large cell sizes, diatoms tolerate iron limitation and frequently dominate iron-stimulated phytoplankton blooms, both natural and artificial. Here, we review the main iron use strategies of diatoms, including their ability to assimilate and store a range of iron sources, and the adaptations of their photosynthetic machinery and architecture to iron deprivation. Our synthesis relies on published literature and is complemented by a search of 82 diatom transcriptomes, including information collected from seven representatives of the most abundant diatom genera in the world’s oceans.

Harmful diatoms and dinoflagellates in the Indian Ocean: a study from Southern coast of Sri Lanka

Harmful diatoms and dinoflagellates in the Indian Ocean: a study from Southern coast of Sri Lanka

Diversity of Epipelic Diatom in The Waters of Tanjung Pinang City Province of Riau Islands

Degradation indicator of water quality can be seen from changes in water quality parameters. Diatoms are one organism that can be used as an environmental bioindicator. Diatoms are the primary producers in waters so they have a very important role in the food chain. Data was collected in situ in the Tanjung Unggat waters of Tanjung Pinang City. The method used in this study is a survey method, where data is obtained through observations and measurements in the field. The samples taken are then taken to the laboratory for analysis. Epiphyte diatom samples were taken from 4 stations with different activities. Based on observations of the identification of diatom epipelic that has been done, found 22 diatom genera, namely, Pleurosigma sp., Navicula sp., Diploneis sp., Achnanthes sp., Synedra sp., Nitzschia sp., Gyrosigma sp., Surirella sp., Coscinodiscus sp., Thallasiossira sp., Thallasionema sp., Pinnularia sp., Plagiotropis sp., Halamphora sp., Biddulphia sp., Melosira sp., Chaetoceros sp., Triceratium sp., Isthmia sp., Licmopora sp., and Rhizosolenia sp. The abundance of diatoms in epipelic samples, which ranged from 905277 - 599530 ind / cm2. The structure of Epipelic Diatom Community average diversity index ranges from 3.72 to 4.65 and the dominance index value ranges from 1.09 to 1.46 and the uniformity index value ranges from 0.95 to 1.21.Then based on the results of the Storet Index classification, getting a score of -52.75 on 8 parameters tested. This scoring means that around the category of Class D Tanjung Pinang Coastal waters with a score ≥ -31 are classified as Heavy Polluted waters with the determination of the status of the waters quality is limited to 8 parameters tested.

Diatom assemblages from sediment traps in response to large seaweed Gracilaria cultivation off Nan'ao island, South China

Most previous studies on seaweed bioremediation largely focus on laboratory control tests or short-time, in-situ field experiments. Here we present a dataset from 4-year-long field monitoring (2014–2018) in a mariculture area of the Baisha Bay off Nan'ao Island, South China, attempting to examine how the large seaweed Gracilaria lemaneiformis cultivation affects a mariculture ecosystem. The temporal variation in seawater physicochemical properties (TN, TP, Reactive silicate, CODMn, and chlorophyll α) and sediment proxies (TN and TP) suggest that the Baisha Bay maintained a better water quality during the Gracilaria cultivation periods (December–May) than other months. Additionally, sedimentary diatom assemblages during the Gracilaria cultivation periods showed an increase in Shannon-Wiener values, but a decrease in the dominant Thalassionema nitzschioides abundance, total diatom abundances and P/(A + B) ratios [Planktonic/(Attached + Benthic)]. These changes consistently suggest that Gracilaria cultivation may have helped improve seawater quality and phytoplankton diversity, thereby maintain a healthy mariculture ecosystem.

Diatom fucan polysaccharide precipitates carbon during algal blooms

The formation of sinking particles in the ocean, which promote carbon sequestration into deeper water and sediments, involves algal polysaccharides acting as an adhesive, binding together molecules, cells and minerals. These as yet unidentified adhesive polysaccharides must resist degradation by bacterial enzymes or else they dissolve and particles disassemble before exporting carbon. Here, using monoclonal antibodies as analytical tools, we trace the abundance of 27 polysaccharide epitopes in dissolved and particulate organic matter during a series of diatom blooms in the North Sea, and discover a fucose-containing sulphated polysaccharide (FCSP) that resists enzymatic degradation, accumulates and aggregates. Previously only known as a macroalgal polysaccharide, we find FCSP to be secreted by several globally abundant diatom species including the genera Chaetoceros and Thalassiosira. These findings provide evidence for a novel polysaccharide candidate to contribute to carbon sequestration in the ocean.

Evaluasi kualitas perairan Sungai Siak di wilayah Kota Pekanbaru berdasarkan kandungan nitrat, posfat dan kelimpahan diatom

Sungai Siak waters is most commonly used by communities Pekanbaru for various activities such as water transportation, fisheries, agriculture, household, industrial and others. While these activities generate waste in the form of partial discharges would enter the river. The purpose of this study was to evaluate the quality of the waters of the Sungai Siak in the city of Pekanbaru based on the content of nitrate and phosphate. The results of measurements of nitrate in the Sungai Siak ranged from 0.2343 to 0.2771 mg/l. Nitrate highest value at Station 4 is 0.3384 mg/l and the lowest at Station 1 is worth 0.2010 mg/l. The content of phosphate in the Siak River which ranged from 1.3932 to 1.5170 mg/l. Great relationship between nitrate with an abundance of diatoms were calculated by correlation coefficient (r) was 0.707 showed a strong association.Great relationship between phosphate with an abundance of diatoms were calculated by correlation coefficient (r) was 0.728 showed a strong association.

Diatom Algae-Indicators of Water Quality in the Lower Zarafshan River, Uzbekistan

This work is the first, the purpose of which was a comprehensive assessment of the ecological state of the lower reaches of the Zarafshan River using bioindication of water quality by diatoms based on species’ ecological preferences, pollution indices, statistics, and ecological mapping. A total of 198 species and subspecies of diatoms were first identified from 195 samples collected four times a year at six sites in the lower reaches of the Zarafshan River in 2009–2015. The richest species were Cymbella, Navicula, and Nitzschia. Pleurosira laevis, resistant to salinity, was first found in aquatic habitats in Uzbekistan. Bioindicators of nine environmental variables make up 91% of the list. Distribution analysis of variables, pollution indices (SLA—SládečDek index of saprobity), and toxicity indices (WESI—Water Ecosystem State Index) show increases in salinity, turbidity, and decreases in organic pollution downstream. The source of acidification can be the Navoi region. We found an increase in the ability to self-purify with an increase in species richness and abundance of diatoms in the lower part of Zarafshan. Thus, the ecosystem of the studied part of the river successfully copes with the incoming pollution from the middle part of Zarafshan and demonstrates some stability and successful self-purification with a water quality class of 2–3. The first studied lower reaches of the ecosystem of the Zarafshan River using bioindicators, statistics, and ecological mapping show that the problem of aridization in Central Asia does not necessarily lead to degradation of the river ecosystem and an increase in pollution, but with rational water use can improve water quality and self-purification processes. Hence, diatoms can be good indicators of river water quality in a semi-arid region and reflect the climate and anthropogenic load change. We recommend that attention be paid to nutrient and turbidity management and to expand state monitoring points to the lower part of the river up to the Karakul region.

Paleo-ecological changes and sedimentary evolution of the Hainan Delta, NW South China Sea

The Hainan Delta, a paleo-delta was penetrated by a 101-meter-long core (ZBW) off the southwestern shore of Hainan Island, in the Beibu Gulf, northwestern South China Sea. Grain size, dinoflagellate cysts, diatoms, and bulk carbon stable isotopes and C/N ratios of the Hainan Delta clearly support four stages of the delta development. Those stages, along the core profile of ca. 74.50–27.0 m below seafloor (mbsf), were reconciled with the deltaic facies; their depth ranges and dates are as follows: 74.50–56.80 mbsf (ca. 65.07–62.01 kyr. BP), 56.80–42.10 mbsf (ca. 62.01–58.61 kyr. BP), 42.10–30.95 mbsf (ca. 58.61–57.02 kyr. BP), and 30.95–27.00 mbsf (ca. 57.02–55.60 kyr. BP). Core ZBW is composed mainly of fine to medium sand, with admixture of coarse sand and shell debris throughout the deltaic facies. The C/N ratio in the sediment indicates mixed terrigenous and marine origin of the organic matter. The bulk carbon isotope record clearly indicates domination of terrigenous sources. The dinoflagellate cyst ('dinocyst') assemblages provided information on in-situ produced marine organic matter delivered to the deltaic sediments. The abundant presence of dinocysts indicates a high nutrient supply and favorable trophic conditions of the waters the donor species dwelled in. A constant supply of organic matter from terrigenous sources and its rapid mineralization is interpreter as factors conducive to a higher abundance of dinocysts. The low abundance of fossil diatoms is attributed to high dilution and the lateral transport of strongly silicified coastal diatoms down the Continental slope.

Spatio-temporal distribution of diatoms and dinoflagellates in the macrotidal Tanintharyi River estuary, Myanmar

The spatio-temporal distribution of diatoms and dinoflagellates composition and abundance were analyzed to investigate their seasonal and neap–spring tidal dynamics in the tide-dominated tropical Tanintharyi River estuary (TRE), Myanmar in 2019. The salinity showed significant variations between seasons (F=32.86, P < 0.001) and the maximum salinity was found in the lower estuary. The turbidity was highest in the mid-upper estuary during spring tide in both seasons. Eighty-two species of microphytoplankton (Fifty-nine species of diatoms and twenty-three species of dinoflagellates) were observed and summarized as 15 groups based on their similarity in cell shapes and sizes. Diatoms were dominant over dinoflagellates in both seasons. The density of diatoms was maximum during the intermediate tide in both seasons. The density of dinoflagellates was maximum during the neap tide in the dry season while during the intermediate tide in the wet season. Spatially, abundances of both diatoms and dinoflagellates were maximum in the lower part of the estuary, which corresponds to high salinity. The abundance of diatoms was significantly different between seasons (F=4.14, P < 0.05). Further, chain-forming diatoms and surface extension dinoflagellates were the dominant groups throughout the estuary. The study indicates that the salinity, turbidity, and mixing driven by the seasons and the neap–spring tidal cycle can influence the distribution and abundance of diatoms and dinoflagellates in the TRE. The cell shape and size promote most aspects of their survival strategy.

Shift in polar benthic community structure in a fast retreating glacial area of Marian Cove, West Antarctica

Glacier retreat is a major long-standing global issue; however, the ecological impacts of such retreats on marine organisms remain unanswered. Here, we examined changes to the polar benthic community structure of “diatoms” under current global warming in a recently retreated glacial area of Marian Cove, Antarctica. The environments and spatiotemporal assemblages of benthic diatoms surveyed in 2018–2019 significantly varied between the intertidal (tidal height of 2.5 m) and subtidal zone (10 and 30 m). A distinct floral distribution along the cove (~ 4.5 km) was characterized by the adaptive strategy of species present, with chain-forming species predominating near the glacier. The predominant chain-forming diatoms, such as Fragilaria striatula and Paralia sp., are widely distributed in the innermost cove over years, indicating sensitive responses of benthic species to the fast-evolving polar environment. The site-specific and substrate-dependent distributions of certain indicator species (e.g., F. striatula, Navicula glaciei, Cocconeis cf. pinnata) generally reflected such shifts in the benthic community. Our review revealed that the inner glacier region reflected trophic association, featured with higher diversity, abundance, and biomass of benthic diatoms and macrofauna. Overall, the polar benthic community shift observed along the cove generally represented changing environmental conditions, (in)directly linked to ice-melting due to the recent glacier retreat.

Orbital and suborbital environmental changes in the Western Bering Sea during the last 172 ka Inferred from Diatom and Productivity Proxies

Abstract Diatom abundance and species distribution present a subtle tool for the reconstruction of the orbital and millennial-centennial climate and environmental changes in the southwestern Bering Sea during the last 172 ka, in addition to productivity proxies (chlorine, color b*, and Ca/Ti ratio), magnetic susceptibility, and biomarker proxies derived earlier and in this paper from the sediment core SO201-2-85KL recovered at the middle Shirshov Ridge (MSR). Available data indicate that the MSR area undergoes a significant seasonal sea ice influence during cold MISs 6.5–2. During the colder MIS 2, a main area of ice discharge extended southward of the MSR, likely outside of the sea, while over the coldest MIS 6.2, the MSR area was free from ice due to the shifting of the Aleutian Low to the eastern Siberian coast and the northward transfer of the warm and wet air of storm tracks into the western Bering Sea. During the warm MIS 5.5, the sea ice influence at the MSR area was negligible, nearly the same as it was over the Holocene, and it began to increase after event 26 (120.5 ka). The millennial scale variability of diatom abundance and its species distribution were triggered by Greenland Interstadials accompanied by productivity changes. The diatom species distribution showed complicated pattern of variability of the MSR environment, consistent with the millennial-centennial changes of the Greenland air temperature over the Dansgaard -Oeschger cycles. It confirms the rapid mechanisms of atmospheric teleconnection between these remote regions on the millennial-centennial time scale.

Оценка связи содержания хлорофилла и биогенных элементов в крупных равнинных водохранилищах

Оценка связи содержания хлорофилла и биогенных элементов в крупных равнинных водохранилищах

Обогащение биогенными веществами и его влияние на сообщество фитопланктона р. Раздан на территории г. Ереван, Республика Армения

The phytoplankton community and nutrient enrichment of Hrazdan River have been studied in the Yerevan District, Republic of Armenia. Water was sampled in spring and summer of 2019. The content of phosphate, ammonium, and nitrite ions were significantly higher downstream of the Yerevan District compared to the stations located upstream. The latter were characterized by higher abundance of diatoms (Melosira varians and Rhoicosphenia curvata), while Oscillatoria limnetica, O. chlorina, and Anabaena sphaerica dominated downstream, reflecting different eutrophic state of the river parts.

Nitrate respiration and diel migration patterns of diatoms are linked in sediments underneath a microbial mat.

Diatoms are among the few eukaryotes known to store nitrate (NO3 - ) and to use it as an electron acceptor for respiration in the absence of light and O2 . Using microscopy and 15 N stable isotope incubations, we studied the relationship between dissimilatory nitrate/nitrite reduction to ammonium (DNRA) and diel vertical migration of diatoms in phototrophic microbial mats and the underlying sediment of a sinkhole in Lake Huron (USA). We found that the diatoms rapidly accumulated NO3 - at the mat-water interface in the afternoon and 40% of the population migrated deep into the sediment, where they were exposed to dark and anoxic conditions for ~75% of the day. The vertical distribution of DNRA rates and diatom abundance maxima coincided, suggesting that DNRA was the main energy generating metabolism of the diatom population. We conclude that the illuminated redox-dynamic ecosystem selects for migratory diatoms that can store nitrate for respiration in the absence of light. A major implication of this study is that the dominance of DNRA over denitrification is not explained by kinetics or thermodynamics. Rather, the dynamic conditions select for migratory diatoms that perform DNRA and can outcompete sessile denitrifiers.

Phytoplankton community structure in a contrasting physico-chemical regime along the eastern Arabian Sea during the winter monsoon

Abstract The paper describes the community composition of phytoplankton in the eastern Arabian Sea (EAS) during winter monsoon (WM, January–February 2018), encompassing the entire eastern part of the Arabian Sea basin (~6–22°N and 77–67°E) with high-resolution sampling (7 transects, 56 sites), from coastal to offshore regions. The phytoplankton pigment concentrations estimated by high-performance liquid chromatography were interpreted using ‘CHEMTAX’ (Mackey et al., 1996) to determine relative abundance and contribution of phytoplankton functional groups at the class level. A distinct spatial heterogeneity was observed in the distribution of phytoplankton groups in the coastal and offshore regions of the northern as well as southern part of the EAS. The basin-scale column integrated chlorophyll a (Chl a) concentration in the upper 100 m was higher (16–118 mg m−2) in the northeastern Arabian Sea (NEAS) as against 9–79 mg m−2 in the southeastern Arabian Sea (SEAS). The chromatographic analysis revealed the dominance of diatoms in the coastal waters of the EAS basin. A closer evaluation of the hydrodynamics and nutrient chemistry of the offshore regions revealed that entrainment of sub-halocline nutrients into the sunlit water column through convective mixing supported the dominant cyanobacterial population in the NEAS. In the warm oligotrophic waters of the SEAS, the substantially high NH4+ concentration indicates that the dominant prochlorophytes were sustained by the regenerated production. The dominance of large phytoplankton like diatoms indicates a herbivorous control in the food chain in coastal waters of the EAS. Offshore waters are characterised by large proportions of pico-nano plankton along with considerable micro phytoplankton, which suggests a mixotrophic ecosystem. The statistical analysis showed that the silicate (Si/N ratio) concentration played a major role in controlling the diatom abundance in the coastal areas of the north (south) EAS while temperature and salinity together with nutrients structured the phytoplankton assemblage in the offshore waters during WM.

A record of diatom community response to catchment land-use change in Moreton Bay, Australia

Embayments and the biota they support are highly susceptible to disturbance within adjacent catchments. Examining the timing and magnitude of impacts arising from human-induced disturbance in these systems is often limited due to the absence of long-term monitoring. Moreton Bay in south-eastern Queensland is a shallow embayment that receives inflows from a 21220-km2 catchment. In this study, diatom abundances, pigment (chlorophyll-a, phaeopigments) and biogenic silica concentrations were evaluated in a composite sediment from central Moreton Bay to explore temporal trends in the photosynthetic community. The record extends from 1200 to 2011, incorporating the period of European settlement (c. 1840s) and rapid population growth and urbanisation of the catchment. The record shows that in central Moreton Bay bloom-forming marine diatoms (Thalassiosira, Thalassiothrix, Thalassionema) have increased in relative abundance since the mid-20th century, whereas the dominant benthic diatom (Paralia fenestrata) has declined. This transition most likely occurred in response to the compounding effects of increased delivery of nitrogen, fine sediments and pollutants to Moreton Bay as a consequence of changes in land use. The inferred historical decline in relative contributions of benthic microalgae to total primary production in central Moreton Bay has likely had wide-ranging ecological effects.

Extensive Microbial Processing of Polysaccharides in the South Pacific Gyre via Selfish Uptake and Extracellular Hydrolysis.

Primary productivity occurs throughout the deep euphotic zone of the oligotrophic South Pacific Gyre (SPG), fueled largely by the regeneration of nutrients and thus recycling of organic matter. We investigated the heterotrophic capabilities of the SPG’s bacterial communities by examining their ability to process polysaccharides, an important component of marine organic matter. We focused on the initial step of organic matter degradation by measuring the activities of extracellular enzymes that hydrolyze six different polysaccharides to smaller sizes. This process can occur by two distinct mechanisms: “selfish uptake,” in which initial hydrolysis is coupled to transport of large polysaccharide fragments into the periplasmic space of bacteria, with little to no loss of hydrolysis products to the external environment, and “external hydrolysis,” in which low molecular weight (LMW) hydrolysis products are produced in the external environment. Given the oligotrophic nature of the SPG, we did not expect high enzymatic activity; however, we found that all six polysaccharides were hydrolyzed externally and taken up selfishly in the central SPG, observations that may be linked to a comparatively high abundance of diatoms at the depth and location sampled (75 m). At the edge of the gyre and close to the center of the gyre, four of six polysaccharides were externally hydrolyzed, and a lower fraction of the bacterial community showed selfish uptake. One polysaccharide (fucoidan) was selfishly taken up without measurable external hydrolysis at two stations. Additional incubations of central gyre water from depths of 1,250 and 2,800 m with laminarin (an abundant polysaccharide in the ocean) led to extreme growth of opportunistic bacteria (Alteromonas), as tracked by cell counts and next generation sequencing of the bacterial communities. These Alteromonas appear to concurrently selfishly take up laminarin and release LMW hydrolysis products. Overall, extracellular enzyme activities in the SPG were similar to activities in non-oligotrophic regions, and a considerable fraction of the community was capable of selfish uptake at all three stations. A diverse set of bacteria responded to and are potentially important for the recycling of organic matter in the SPG.

Millennial‐scale environmental changes in the northwestern Japan Sea during the last glacial cycle

High‐resolution analyses of pollen and diatoms in core LV 53‐29 from the northwestern Japan Sea trace climate, vegetation and oceanographic changes during the past 120 ka. The age model for the core was based on tephrochronology, colour lightness and magnetic susceptibility and was used to aid correlation with Dansgaard‐Oeschger cycles (warm Greenland interstadials (GIs) and cold Greenland stadials (GSs)). The palynological and diatom data from this core record the changing influences of the East Asian monsoon, eustatic fluctuations in sea level, and the impact of variations in the direction and intensity of marine currents. Increases in Quercus and Cryptomeria pollen reflect GIs. The highest values of Cryptomeria were recorded during Marine Isotope Stage (MIS) 5 and were associated with an increase in the intensity of the summer monsoon. The increase in Larix pollen is an indicator of GSs, and it occurs in all marine isotopic stages. Changes in diatom records indicate that oceanographic conditions in the northwestern Japan Sea differed from its southern and eastern regions. An increase in the cold‐water and polyhalobous Rhizosolenia hebetata indicates GIs, although the surface water temperatures were colder than today with normal salinity. Species of the genus Chaetoceros, which is characteristic of GSs, were abundant during MIS 2. The predominance of Chaetoceros taxa and the high total abundance of diatoms may reflect regional upwelling conditions. The absence of brackish‐water species at this time indicates a slight freshening of the surface water. The study of pollen, spores and diatoms in sediments from the northwestern Japan Sea illustrates the great potential of these proxies for identifying abrupt climate oscillations preserved in high‐temporal resolution marine records, particularly those related to interstadial and stadial conditions.

Sea ice dynamics in the Bransfield Strait, Antarctic Peninsula, during the past 240 years: a multi-proxy intercomparison study

Abstract. In the last decades, changing climate conditions have had a severe impact on sea ice at the western Antarctic Peninsula (WAP), an area rapidly transforming under global warming. To study the development of spring sea ice and environmental conditions in the pre-satellite era we investigated three short marine sediment cores for their biomarker inventory with a particular focus on the sea ice proxy IPSO25 and micropaleontological proxies. The core sites are located in the Bransfield Strait in shelf to deep basin areas characterized by a complex oceanographic frontal system, coastal influence and sensitivity to large-scale atmospheric circulation patterns. We analyzed geochemical bulk parameters, biomarkers (highly branched isoprenoids, glycerol dialkyl glycerol tetraethers, sterols), and diatom abundances and diversity over the past 240 years and compared them to observational data, sedimentary and ice core climate archives, and results from numerical models. Based on biomarker results we identified four different environmental units characterized by (A) low sea ice cover and high ocean temperatures, (B) moderate sea ice cover with decreasing ocean temperatures, (C) high but variable sea ice cover during intervals of lower ocean temperatures, and (D) extended sea ice cover coincident with a rapid ocean warming. While IPSO25 concentrations correspond quite well to satellite sea ice observations for the past 40 years, we note discrepancies between the biomarker-based sea ice estimates, the long-term model output for the past 240 years, ice core records, and reconstructed atmospheric circulation patterns such as the El Niño–Southern Oscillation (ENSO) and Southern Annular Mode (SAM). We propose that the sea ice biomarker proxies IPSO25 and PIPSO25 are not linearly related to sea ice cover, and, additionally, each core site reflects specific local environmental conditions. High IPSO25 and PIPSO25 values may not be directly interpreted as referring to high spring sea ice cover because variable sea ice conditions and enhanced nutrient supply may affect the production of both the sea-ice-associated and phytoplankton-derived (open marine, pelagic) biomarker lipids. For future interpretations we recommend carefully considering individual biomarker records to distinguish between cold sea-ice-favoring and warm sea-ice-diminishing environmental conditions.