Sea surface conditions in the southern Nordic Seas during the Holocene based on dinoflagellate cyst assemblages

Abstract

Dinoflagellate cyst (dinocyst) records from the southern Nordic Seas were compiled in order to evaluate the evolution of upper ocean conditions, on a millennial timescale and supported by a highly resolved record from the Vøring Plateau. After the transitional phase from the last deglaciation, three main phases define the Holocene. The early Holocene (>7.5 ka BP) features important numbers of cool-temperate species dominated by Nematosphaeropsis labyrinthus and Impagidinium pallidum in the west. The assemblage composition changes drastically at the transition from the early to the mid-Holocene, from when on Operculodinium centrocarpum dominates. The changeover is dated between ~6.1 and 7.5 ka BP, perhaps earlier closer to the Iceland–Scotland Ridge, and appears to be linked to the onset of a modern type of surface circulation. ‘Warmest’ assemblages occur at the Vøring Plateau shortly after the transition, when Atlantic waters also appear to have spread farthest westward. The recurrence of colder elements can be linked to cooling from ~2.4 ka BP at the Vøring Plateau and presumably earlier in the west but is difficult to date there because of the low sedimentation rates. This is a general issue in many areas of the Nordic Seas and appears to have an important effect on cyst concentrations and assemblage composition, with the possible loss of oxygenation-sensitive cysts in the older parts of the cores. Comparing dinocyst-based quantitative reconstructions with those retrieved from other plankton reveals a significantly different trend between proxies, linked to a differing autecological response to seasonal changes at their respective depth habitats.

Climate variability in the subarctic area for the last 2 millennia

“…38 show a significant decrease (τ = −0.18, p < 0.01), whereas those from record 39 present a slight, but non-significant increase (τ = 0.14, p = 0.14). Different sensitivity to seasonal temperatures possibly explains the difference between the two records as previously reported from the Nordic Seas (Van Nieuwenhove et al, 2016). In the Arctic-subarctic areas, diatoms often relate to a spring bloom, whereas alkenones are produced by coccolithophorids, which develop during the warmest part of the summer (e.g., Andruleit, 1997).…”

“…The three regional time series calculated and used in the paper are available at https://doi.org/10.6084/m9.figshare.5616310. The wavelet transform (WA) is particularly adapted for the study of nonstationary processes, i.e., discontinuities and changes in frequency or magnitude (Torrence and Compo, 1998). Wavelet analysis corresponds to a band-pass filter, which decomposes the signal on the base of scaled and translated versions of a reference wave function.…”

“…Detected fluctuations are statistically tested at the α = 0.05 significance level against an appropriate background spectrum, i.e., a red noise (autoregressive process for AR(1) > 0) or a white noise (autoregressive process for AR(1) = 0) background (Torrence and Compo, 1998). Autoregressive modeling is used to determine the AR(1) stochastic process for each time series.…”

Sea surface density gradients in the Nordic Seas during the Holocene as revealed by paired microfossil and isotope proxies

“…in the western cores and illustrates the reorganization of the upper ocean across the southern Nordic Seas around that time (Figures and ) [cf. Van Nieuwenhove et al ., ].…”

Islandinium minutum subsp. barbatum subsp. nov. (Dinoflagellata), a New Organic‐Walled Dinoflagellate Cyst from the Western Arctic: Morphology, Phylogenetic Position Based on SSU rDNA and LSU rDNA, and Distribution

“…; Van Nieuwenhove et al. ). The family Protoperidiniaceae is known to produce a large proportion of the RBSCs (Fukuyo et al.…”