Diatom Record Research Articles

Long-term and regional perspectives on recent change in lacustrine diatom communities in the tropical Andes

Understanding and managing the responses of natural systems to climate change requires knowing whether recent changes in ecosystem structure and function are within the bounds of natural variation or whether the systems are entering new states that are unprecedented. Several recent studies of the fossil diatom record of the last ~ 150 years in Andean lakes have shown changes in diatom species composition that suggest changes in lake thermal structure in response to regional climate warming. Yet these paleolimnological records are only a few hundred years in length, so it is unclear whether the systems have entered new states, with potentially severe consequences for ecosystem structure and function, or whether current trends are within the natural variability of the systems. Here, we use a recently compiled diatom database from tropical South America to explore the regional distribution and ecological controls of selected planktic diatom taxa that are associated with warming and changes in the lake thermal structure. We also review published Andean stratigraphic records that span thousands of years to characterize the long-term dynamics of relevant planktic species in response to past climate change. The contemporary data show that many planktic taxa have broad latitudinal and elevational distributions. The distributions of several taxa are correlated with surface water temperature, but most also are correlated with pH and/or conductivity. A review of existing stratigraphic data from Andean lakes demonstrates that rapid changes in diatom abundance, including abrupt increases followed by decades to centuries of near extirpation, are a common mode of population variation for some planktic taxa. Yet the majority of these published paleolimnological investigations are of lakes that are larger and differ in nutrient status and conductivity from the small dilute systems where recent species shifts have been observed. We propose that assessing the resilience of contemporary diatom communities and, by inference, lake ecosystems is best done by generating new records from Andean lakes of varied size and chemistry that span a millennium or more and hence a broader spectrum of climate conditions, coupled with new ecological and biogeographic studies that build upon ongoing research programs in the tropical Andes. (Less)

New insights into the termination of the African Humid Period (5.5 ka BP) in central Ethiopia from detailed analysis of a diatom record

The termination of the African Humid Period in northern Africa has been described as abrupt, occurring within centuries, as well as gradual, in response to incremental decreases in summer insolation. This study examined the rapidity of the change in diatom assemblages over the period from 6.5 to 4.5 cal ka BP, in a core studied previously at a coarser resolution. This transition was characterized by high variability of assemblages, which could be related, in part, to changes in water conductivity, and potentially enhanced by a site-specific hydrological threshold or ecological salinity threshold. We hypothesize that the variations in diatom assemblages reflect climate fluctuations, which may have been an early warning signal of an impending climate regime shift.

The Paleocene record of marine diatoms in deep-sea sediments

Abstract. Marine planktonic diatoms, as today's ocean main carbon and silicon exporters, are central to developing an understanding of the interplay between the evolution of marine life and climate change. The diatom fossil record extends as far as the Early Cretaceous, and the late Paleogene to Recent interval is relatively complete and well documented. Their early Paleogene record, when diatoms first expanded substantially in the marine plankton, is hampered by decreased preservation (notably an episode of intense chertification in the early Eocene) as well as by observation bias. In this article, we attempt to correct for the latter by collecting diatom data in various Paleocene samples from legacy Deep Sea Drilling Project and Ocean Drilling Program deep-sea sediment sections. The results show a different picture from what previous analyses concluded, in that the Paleocene deep-sea diatoms seem in fact to have been as diverse and abundant as in the later Eocene, while exhibiting very substantial survivorship of Cretaceous species up until the Eocene.

Late Holocene climatic variability in Subarctic Canada: Insights from a high-resolution lake record from the central Northwest Territories.

We examined late Holocene (ca. 3300 yr BP to present-day) climate variability in the central Northwest Territories (Canadian Subarctic) using a diatom and sedimentological record from Danny’s Lake (63.48ºN, 112.54ºW), located 40 km southwest of the modern-day treeline. High-resolution sampling paired with a robust age model (25 radiocarbon dates) allowed for the examination of both lake hydroecological conditions (30-year intervals; diatoms) and sedimentological changes in the watershed (12-year intervals; grain size records) over the late Holocene. Time series analysis of key lake ecological indicators (diatom species Aulacoseira alpigena, Pseudostaurosira brevistriata and Achnanthidium minutissimum) and sedimentological parameters, reflective of catchment processes (coarse silt fraction), suggests significant intermittent variations in turbidity, pH and light penetration within the lake basin. In the diatom record, we observed discontinuous periodicities in the range of ca. 69, 88–100, 115–132, 141–188, 562, 750 and 900 years (>90% and >95% confidence intervals), whereas the coarse silt fraction was characterized by periodicities in the >901 and <61-year range (>95% confidence interval). Periodicities in the proxy data from the Danny’s Lake sediment core align with changes in total solar irradiance over the past ca. 3300 yr BP and we hypothesize a link to the Suess Cycle, Gleissberg Cycle and Pacific Decadal Oscillation via occasional inland propagation of shifting air masses over the Pacific Ocean. This research represents an important baseline study of the underlying causes of climate variability in the Canadian Subarctic and provides details on the long-term climate variability that has persisted in this region through the past three thousand years.

Late Holocene climate changes from diatom records in the historical Reservoir Gonggeomji, Korea

The paleoenvironmental history of the artificial Reservoir Gonggeomji in Sangju City, Korea, was reconstructed using fossil diatom analysis of four sediment cores: GG01, 02, 03, and 04. Accelerator mass spectrometer (AMS) radiocarbon dating results suggest that Reservoir Gonggeomji was maintained from ca. 1350 to 150 cal year BP, and the diatom record in core sediment samples revealed well-defined hydrological changes and paleoenvironmental conditions during this period. The fossil diatom assemblages were predominantly benthic freshwater diatoms. The highest diatom concentrations in all cores were in diatom zone II, in which species richness and diversity were also very high. Cymbella, Eunotia, Gomphonema, Gyrosigma, Navicula, and Pinnularia were the dominant genera in all core sediments. The long-term trend in diatom species abundance and species diversity showed a stronger relationship to temperature anomalies in the northern hemisphere during the past 2000 years with changes in precipitation. These diatom changes could have been controlled by natural climate change, despite anthropogenic activities linked to construction of the dyke in the artificial reservoir.

Diatom record of progressive anthropopressure in the Gulf of Gdańsk and the Vistula Lagoon

Abstract This study describes the subfossil diatom flora in the surface sediments of the Polish coastal waters in relation to human impact. The material studied consists of the uppermost parts of seven sediment cores collected from the SW Gulf of Gdańsk and eight cores from the Vistula Lagoon. Our results show the present-day ecological state of both basins just before the planned construction of a navigable channel of the Vistula Spit, which will be the next factor affecting their hydrology. In different parts of the Gulf of Gdańsk, cultural eutrophication resulted in a distinct “anthropogenic assemblage” in the surface sediments. Its structure relates directly to the distance from the mouth of the Vistula River. In the surface assemblages of the Vistula Lagoon, the number of salt-tolerant diatoms increased with the salinity of the basin. Locally, a large number of pollution-resistant taxa was also observed.

Using a decadal diatom sediment trap record to unravel seasonal processes important for the formation of the sedimentary diatom signal

Sediment trap studies and high frequency monitoring are of great importance to develop a deeper understanding of how seasonal environmental processes are imprinted in sediment signal formation. We collected whole year diatom assemblages from 2002 to 2014 with a sequential sediment trap from a varved boreal lake (Nylandssjön, Sweden) together with environmental and limnological parameters, and compared them with the corresponding diatom record of the annual laminated sediment. Our data set indicates a large year-to-year variability of diatom succession and abundance patterns, which is well reflected in the varved sediments. Specifically, Cyclotella glomerata dominated the annual sediment trap record (as well as in the corresponding sediment varves) in years with warmer air temperatures in March/April, and Asterionella formosa dominated the annual sediment assemblages as a consequence of years characterized by higher runoff before lake over-turn. Years succeeding forest clearance in the lake catchment showed marked increase in diatom and sediment flux. The DCA scores of the yearly diatom trap assemblages clearly resemble the lake’s thermal structure, which indicates that the relative abundance of major taxa seems primarily controlled by the timing of seasonal environmental events, such as above-average winter air temperature and/or autumn runoff and the current thermal structure of the lake. The high seasonal variability between environmental drivers in combination with the physical limnology leaves us with several possible scenarios leading to either an A. formosa versus C. glomerata dominated annual diatom sediment signal. With this study we highlight that short-term environmental events and seasonal limnological conditions are of major importance for interpreting annual sediment signals.

Multi‐proxy reassessment of the paleolimnology of Lake Bonneville (western USA) as observed in the restricted Pilot Valley sub‐basin

ABSTRACTLate Pleistocene sediments of pluvial Lake Bonneville of the western USA represent an important archive of climate and paleolimnological processes. Geochemical, mineralogical and diatom records from the Pilot Valley sub‐basin represent a complete multi‐proxy record of the Bonneville cycle, including closed‐basin transgressive, the Bonneville flood, open‐lake and closed‐basin regressive cycles. Diatoms record pH and salinity, and vary from alkalibiontic/brackish (early transgression), alkaliphilous/fresh‐brackish (deep lake) and back to alkalibiontic/brackish (late regression) conditions. Pennate diatoms reveal passage through and back into the euphotic zone due to the penetration of light through the water column supporting an active benthos. As such, the base of the euphotic zone (∼35 m depth) can be established through time. Restriction and evaporation within the Pilot Valley arm of Lake Bonneville during times of shallow water produced very high endogenic carbonate production, an order of magnitude higher than during deep water. This is shown by age–depth relations in the core, major element and isotopic variations, and sediment mineralogy, requiring a major re‐evaluation of the position of the Bonneville flood horizon within the sediments of Pilot Valley. In summary, lacustrine sediments from restricted arms of large pluvial lakes may vary significantly from complementary records from an open basin.

Diatom-based inference of Asian monsoon precipitation from a volcanic lake in southwest China for the last 18.5 ka

Diatom in the volcanic lake provides proxy evidence for pH changes that are characterized by variations in the percentage of acidophilous diatom species. The information regarding the hydrology of the lake, derived from a previous publication and survey of one year on the lake, indicate that pH is low during the wet season and higher during the dry season. Therefore, variations in lake water pH may be considered as a proxy record for past changes in precipitation. In the sediment, high/low relative abundance of acidophilous diatom species indicates high/low precipitation. The diatom record of the past 18.5 ka BP shows that precipitation decrease during the periods 17.0–15.0, 13.3–11.3, and 0.7–0.3 ka BP corresponding to the Heinrich Event 1 (H1), the Younger Dryas cold event (YD), and the Little Ice Age (LA). A marked precipitation increase between 15.0 and 14.5 ka BP occurred at the end of H1 and before the Bølling-Allerød (BA), which indicates a strong pre-Bølling wetting. The start of the Holocene is recorded at 11.3 ka BP. The climate was the wettest between 11.3 and 7.5 ka BP., then the wetter between 7.5 and 3.4 ka BP. Between 3.4 and 0.7 ka BP, the precipitation decrease in general, but in the period from 1.3 to 0.8 ka BP the precipitation was higher corresponding to the Medieval Warm Period (MWP). Our results support the hypothes that the Indian Summer Monsoon (ISM) was strongest during the Early Holocene.

First record of middle Miocene marine diatoms from the Colombian Pacific (NW South America) and their paleoceanographic significance

Abstract Middle Miocene marine diatoms have been reported in the eastern equatorial Pacific by the Deep Sea Drilling Project (DSDP), the Ocean Drilling Program (ODP), and the Integrated Ocean Drilling Program (IODP); few studies, however, have been completed on onshore sections from South America. Vallejo et al. (2006) published the biostratigraphy of the Ladrilleros-Juanchaco section on the northwest Pacific Colombian coast utilizing calcareous nannofossils, planktonic foraminifera and diatoms. In this work we present in detail the study of marine diatoms of that section in order to understand their implications with the age model proposed and provide a paleoceanographic interpretation. The diatom recovery is restricted to two intervals at the top of the Miocene sequence. Two biozones from the low latitude zonation can be recognized; from base to top they are: 1) The Coscinodiscus lewisianus Zone, which contains the same species assemblage reported in Antofagasta coastal sediments, Chile; and 2) the Craspedodiscus coscinodiscus Zone. We found that the diatoms represent older ages than proposed by calcareous nannofossils. These different ages suggest diachronism between the events of microfossil groups. Nevertheless, in a new interpretation of the distribution patterns of calcareous nannofossils in the upper part of the section, the diatom age model could be synchronous. The high abundance of Thalassionema nitzschioides and Thalassiothrix longissima reveal cool, upwelling-rich oceanic waters at the top of the sequence, as well as an increase in paleoproductivity suggested by an increase of Rhizosolenia spp. and T. longissima mats. Cool water trends support a strengthening of the Peru-Chile current. Actinoptychus sp., Leptocylindrus danicus and Paralia sulcata point to a nearshore environment. The common occurrence of fresh water continental diatoms and palm silicophytoliths indicate an increased input of continental material. Since ichnofossils and benthic foraminifera reveal ocean depths below 1000 m, this change may have related to hyperpycnal flows.

East Asian Winter Monsoon Variations and Their Links to Arctic Sea Ice During the Last Millennium, Inferred From Sea Surface Temperatures in the Okinawa Trough

AbstractThe East Asian winter monsoon (EAWM) significantly impacts living conditions in a large part of Asia, and therefore, it is important to understand its major driving mechanisms. Winter sea surface temperature (SSTW) and circulation in the southern Okinawa Trough are today both primarily controlled by the EAWM. Here we present a new SSTW reconstruction for the last millennium based on a diatom record from sediment core MD05‐2908, from the continental slope of the southern Okinawa Trough off northeastern Taiwan. Our reconstruction indicates that SSTW varied between 14.1 and 19.6°C over the past 1,000 years. Changes in SSTW in the southern Okinawa Trough correspond closely to the index of warm winters based on historical documents from the East Asian monsoon domain. This implies that our SSTW record can be used to reconstruct EAWM variability during the last millennium. Comparisons with the reconstructed winter Arctic Oscillation (AO, developed from historical snow anomaly events in Eastern Asia) and Arctic sea ice cover reveal a significant positive correlation between the EAWM and AO during the time interval from 1000–1400 Common Era (C.E.), coinciding with reduced sea ice cover. However, there is no significant correlation with increased sea ice cover during the interval from 1400 to 1700 C.E. This suggests that the reduction in Arctic sea ice may periodically have played a role in strengthening the relationship between the EAWM and the AO during the last millennium and that the current and future reduction in Arctic sea ice may have significant consequences for the EAWM.

Diatom response to climatic warming over the last 200 years: A record from Gonghai Lake, North China

Annual monitoring data and centennial and millennial-scale paleolimnological records have revealed an increase in small-celled planktonic diatom species relative to heavier tycho-planktonic and small benthic diatoms in many high-altitude lakes, presumably in response to recent climatic warming. In addition to changes in the composition and structure of lacustrine diatom assemblages, there have also been changes in diatom biodiversity; however, these changes are not regionally consistent. In this study, we chose a temperate mid-latitude lake to explore the response of changes in diatom assemblages and biodiversity to recent climatic warming. The diatom record spans the past ca. 200years and reveals that since 1966 CE the small-celled Cyclotella ocellata+stelligera has replaced the previously dominant, large-celled phytoplankton Cyclotella schroeteri. These changes are in accordance with the increasing trend in global mean surface temperature. Biodiversity increased remarkably from 1966 CE, but began to decline after 1990 CE, presumably in response to rapid climatic warming. Our findings indicate that the response of diatom biodiversity to climate change was a nonlinear process.

Glacial and interglacials in the Neotropics: a 130,000-year diatom record from central Panama

The last interglacial was the most recent time when temperatures were 1–2 °C above modern, but little is known of this period in the lowland Neotropics. Equally, data for the full glacial period are very limited. A detailed analysis of the period between ~ 137 and 100 ka was completed to provide a paleoecological history of the last interglacial in central Panama. Two additional fossil diatom records from the same depositional basin provided records of the glacial period. Diatom assemblages were compared across all cores and the dominant species of both glacial and interglacial periods was almost always Aulacoseira granulata. Other species, e.g. Aulacoseira agassizii, Achnanthidium minutissimum, Nitzschia amphibia, and Navicula radiosa, had distinctive patterns of abundance within the record, indicating a shallowing of the lake in the last millennia of MIS5e. The period between 119 and 108 ka witnessed the most change within the high-resolution portion of the record suggesting an increased lake level, with expanding lake margins. Other sediment cores collected within the caldera revealed the continued presence of a lake at El Valle through much of the glacial period, with shallowing evident at the time of the LGM. The changes in diatom assemblages at El Valle provide one of the oldest precipitation records from Central America tracking mean ITCZ position between the last interglacial and glacial periods. Furthermore, the evidence for both a wet interglacial and glacial period support palynological findings that the humid environments of Central Panama were not interrupted by glacial aridity.

A diatom record of CO2 decline since the late Miocene

Extratropical sea surface temperature records from alkenones record a dramatic cooling of up to 17 °C over the last ∼14 Ma, but the relationship between this cooling and greenhouse gas forcing has been elusive due to sparse and contrasting reconstructions of atmospheric CO2 for the time period. Alkenone carbon isotopic fractionation during photosynthesis has previously been used to estimate changes in pCO2 over this interval, but is complicated by significant changes in cell size of the alkenone-producing coccolithophorids over this time period. In this study, we reconstruct carbon isotopic fractionation during photosynthesis (εp) using organic compounds trapped within the frustules of pennate diatoms in sediments from the Eastern Equatorial Pacific Ocean at Ocean Drilling Program Site 846 over the last ∼13 Ma. Physical separation of pennate diatoms prior to measuring carbon isotopic fractionation enables us to obtain a record with constant cell geometry, eliminating this factor of uncertainty in our pCO2 reconstruction. In the past ∼11 Ma, εp declines from 15.5 to 10.3‰. Using the classic diffusive model and taking into account variations in opal content, alkenone concentration and coccolith Sr/Ca as indicators of past productivity and growth rate, and sea surface temperature records from the site, we estimate a decline in pCO2 from 454 (+/−41) to 250 (+/−15) ppmv between ∼11 and 6 Ma. Models accounting for changing the significance of active carbon uptake for photosynthesis, which likely produce more accurate CO2 estimates, suggest a significant larger pCO2 decline of up to twice that shown by the classic diffusive model (in average from 794 (+/−233) ppmv at ∼11 Ma to 288 (+/−25) ppmv at ∼6 Ma, considering growth rates varying between 0.5 and 1.7 day−1). Large uncertainties in the pCO2 estimated between ∼8 and 11 Ma using the active uptake model are related to the growth rate used for calculations. Together, these results suggest CO2 forcing for this period of steep decline in temperatures.

High-resolution diatom record of paleoceanographic variations across the Early–Middle Pleistocene boundary in the Chiba Section, central Japan

We conducted diatom analyses of a core from the Pleistocene marine sequence drilled at the Chiba Section, central Japan, to reveal detailed paleoceanographic variations across the Early–Middle Pleistocene boundary. Diatom valves are most abundant at 4.5 m below the Matuyama–Brunhes magnetic polarity boundary, followed by the second highest abundance at 18.6 m above the boundary, which is consistent with the sea-level changes inferred from planktonic δ18O data. The highest abundance is correlated with the Marine Isotope Stage (MIS) 19.3 sea-level highstand, and the second-highest with the MIS 19.1 highstand. The abundance of the extinct species Actinocyclus ingens is quite low around these sea-level highstands, whereas it is greatest at the core depth with the minimum diatom total valves, which is correlated to the MIS 19.2 lowstand. Cold-water diatom species that are characteristic of the Oyashio Current are dominant but coexist with warm-water species of the Kuroshio Current below a core depth just postdating MIS 19.2. Above this depth, warm diatom species of the Kuroshio Current become dominant. The change in dominant diatoms suggests that the Kuroshio Front shifted northward just after MIS 19.2 and remained in the northern area until at least early MIS 18. This shift caused a rapid increase in sea-surface temperature by 4–5 °C within a sediment thickness of 1.3 m (representing ∼300 years).

The response of the Bering Sea Gateway during the Mid-Pleistocene Transition

The Mid-Pleistocene transition and the response of sea ice in the subarctic North Pacific are examined using a diatom record from the north eastern Bering Sea slope (IODP core U1344A). High percentages of diatom sea ice species in the assemblage foster the development of groupings specific to differing ice conditions. Thalassiosira antarctica var. borealis emerges as a key diatom species that delineates the development of thick multiannual sea ice and marks a series of advancements from 0.9 to1.2Ma after which it dominates the assemblage until 0.6Ma. The decline of Neodenticula seminae, indicative of Alaskan Stream water inflow, is in agreement with neighbouring core U1343E confirming the reduction of Bering Sea circulation after 0.9Ma. We propose that during the MPT a stepped advancement of sea ice occurs in the Bering Sea as a response to increased moisture delivery to the high latitudes. An extended period of diatom productivity between 0.75 and 0.65Ma, marks major deglacial conditions towards the end of the MPT by 0.6–0.55Ma. The work highlights the important role played by sea ice and supports the contention of a colder MPT in the subarctic Pacific.

A ~6000 yr diatom record of mid- to late Holocene fluctuations in the level of Lago Wiñaymarca, Lake Titicaca (Peru/Bolivia)

AbstractA multidecadal-scale lake-level reconstruction for Lago Wiñaymarca, the southern basin of Lake Titicaca, has been generated from diatom species abundance data. These data suggest that ~6500 cal yr BP Lago Wiñaymarca was dry, as indicated by a sediment unconformity. At ~4400 cal yr BP, the basin began to fill, as indicated by the dominance of shallow epiphytic species. It remained somewhat saline with extensive wetlands and abundant aquatic plants until ~3800 cal yr BP, when epiphytic species were replaced by planktic saline-indifferent species, suggesting a saline shallow lake. Wiñaymarca remained a relatively shallow lake that fluctuated on a multidecadal scale until ~1250 cal yr BP, when freshwater planktic species increased, suggesting a rise in lake level with a concomitant decrease in salinity. The lake became gradually fresher, dominated by deep, freshwater species from ~850 cal yr BP. By ~80 cal yr BP, saline-tolerant species were rare, and the lake was dominated by freshwater planktic diatoms, resembling the fresh and deep lake of today. These results reveal a more dynamic and chronologically specific record of lake-level fluctuations and associated ecological conditions that provide important new data for paleoclimatologists and archaeologists, to better understand human-environmental dynamics during the mid- to late Holocene.

On the Age and Origin of Lake Ejagham, Cameroon, and Its Endemic Fishes

AbstractLake Ejagham is a small, shallow lake in Cameroon, West Africa, which supports five endemic species of cichlid fishes in two distinct lineages. Genetic evidence suggests a relatively young age for the species flocks, but supporting geologic evidence has thus far been unavailable. Here we present diatom, geochemical, mineralogical, and radiocarbon data from two sediment cores that provide new insights into the age and origin of Lake Ejagham and its endemic fishes. Radiocarbon ages at the base of the longer core indicate that the lake formed approximately 9 ka ago, and the diatom record of the shorter core suggests that hydroclimate variability during the last 3 millennia was similar to that of other lakes in Cameroon and Ghana. These findings establish a maximum age of ca. 9 cal ka BP for the lake and its endemic species and suggest that repeated cichlid speciation in two distinct lineages occurred rapidly within the lake. Local geology and West African paleoclimate records argue against a volcanic, chemical, or climatic origin for Lake Ejagham. Although not conclusive, the morphometry of the lake and possible signs of impact-induced effects on quartz grains are instead more suggestive of a bolide impact.

A &gt;22,000 yr diatom record from the plateau of Zambia

AbstractDiatoms and sediments were examined in a 530 cm core from Ishiba Ngandu, Zambia, a lake formed by gentle downwarping. Diatom zone D (&gt;20 cal ka BP) was mostly sand with abundantAulacoseiraandEunotia, suggesting a shallow lake perhaps kept fresh by spring inputs and lake discharge, except during deposition of the lowermost 66 cm. Gyttja deposition between about 22 and 20 cal ka BP suggested a deeper lake and a wetter climate, perhaps because the Congo Air Boundary (CAB) was farther southeast relative to modern times. The next zone, zone C (about 20–19 cal ka BP), was sand with abundantAchnanthidiumandEunotiabut very few planktonic diatoms, apparently representing very shallow water and an arid period without the CAB. The gyttja and diatoms in zone B (19–4 ka) suggested an increase in moisture when the CAB returned. Zone A (4–0 cal ka BP) was dominated by the planktonicAulacoseira(&gt;89%), suggesting an increase in wind-driven mixing. Uniquely, Ishiba Ngandu likely has been relatively moist since the last glacial maximum, matching pre-Holocene wetness in Botswana but not its Holocene aridity; evidently the climate here had switched to that of East Africa.

Impacts of late‐Holocene climate variability and watershed‐lake interactions on diatom communities in Lac Brûlé, Québec

AbstractA high‐resolution diatom analysis of a varved sediment sequence from Lac Brûlé, southwestern Québec, was used to study temporal patterns of environmental change in the late Holocene. Key periods of interest in the record included the Medieval Warm Period (~800–1300 CE), the Little Ice Age (~1450–1850 CE), and post‐European settlement (~1850–present). Subfossil diatom assemblages were compared to previously published pollen, cladocera, and sediment records from Lac Brûlé, revealing complex dynamics between terrestrial vegetation succession, nutrient fluxes, and trophic interactions. Generalized additive models showed a response to long‐term climate variability in the diatom record, although it was not the most influential driver of community changes at Lac Brûlé. Catchment‐mediated processes instead played the largest role in governing the structure of diatom assemblages in the lake. For example, nutrient loading following a local fire in the watershed at 1345 CE led to an abrupt and significant increase in Fragilaria spp. Human activity associated with deforestation and the Wallingford‐Back Mine (1924–1972 CE) also had strong impacts on the landscape, which triggered further responses in the aquatic communities of Lac Brûlé.