New Magnetostratigraphic Insights From Iceberg Alley on the Rhythms of Antarctic Climate During the Plio‐Pleistocene

Abstract

International Ocean Discovery Program (IODP) Expedition 382 in the Scotia Sea's Iceberg Alley recovered among the most continuous and highest resolution stratigraphic records in the Southern Ocean near Antarctica spanning the last 3.3 Myr. Sites drilled in Dove Basin (U1536/U1537) have well-resolved magnetostratigraphy and a strong imprint of orbital forcing in their lithostratigraphy. All magnetic reversals of the last 3.3 Myr are identified, providing a robust age model independent of orbital tuning. During the Pleistocene, alternation of terrigenous versus diatomaceous facies shows power in the eccentricity and obliquity frequencies comparable to the amplitude modulation of benthic δ 18 O records. This suggests that variations in Dove Basin lithostratigraphy during the Pleistocene reflect a similar history as globally integrated ice volume at these frequencies. However, power in the precession frequencies over the entire ∼3.3 Myr record does not match the amplitude modulation of benthic δ 18 O records, suggesting Dove Basin contains a unique record at these frequencies. Comparing the position of magnetic reversals relative to local facies changes in Dove Basin and the same magnetic reversals relative to benthic δ 18 O at North Atlantic IODP Site U1308, we demonstrate Dove Basin facies change at different times than benthic δ 18 O during intervals between ∼3 and 1 Ma. These differences are consistent with precession phase shifts and suggest climate signals with a Southern Hemisphere summer insolation phase were recorded around Antarctica. If Dove Basin lithology reflects local Antarctic ice volume changes, REILLY ET AL.

Antiphased dust deposition and productivity in the Antarctic Zone over 1.5 million years

“…4 and 7 ), which is ground-truthed at magnetic reversals (Supplementary Fig. 4 ) 21 . We used this recognition in the next step and further tuned the lower part of the MS record (0.8–1.5 Ma), where no ice-core dust data exists, to glacials in the LR04 record (blue tie points in Fig.…”

“… 6 ) (Fig. 3c, d ) for that period along with maxima in NGR and GRA, (2) the age assignation is ground-truthed at paleomagnetic reversals 21 (Supplementary Fig. 4 ) and (3) dust proxies show close covariation between ice volume and independently dated sea level changes when plotted logarithmically (Fig.…”

“…2 ; Methods, Supplementary Tables 1 and 2 ). Implications for rhythms of Antarctic climate since the Pliocene using this untuned age model are provided by 21 .…”

Expanded North Pacific Subtropical Gyre and Heterodyne Expression During the Mid‐Pleistocene

“…This age model provides strong evidence for a continuous 2.2 Myr record at Hole 1207A with sedimentation rates (average of 1.45 cm/kyr) that resolve orbital variability in a pelagic marine setting that is typical of Cenozoic benchmark studies with analogous sedimentation rates from the Atlantic Ocean sector (e.g., Meyers, 2015;Westerhold et al, 2012;Zachos et al, 2004). The well-resolved magnetostratigraphy and biostratigraphy at the site provide a robust age model independent of orbital tuning, whereby we can assess the imprint of orbital forcing in the framework of lithostratigraphy (e.g., Caballero-Gill et al, 2019;Patterson et al, 2014;Proistosescu et al, 2012;Reilly et al, 2021). Previous studies documenting the occurrence of planktic foraminifera species at this site and within the KCE system indicate that waters above Hole 1207A fluctuated from being in subtropical to subarctic through the late-Neogene in response to tectonic and climate events (Lam & Leckie, 2020a, 2020b.…”

“…Data were resampled at a conservative median sampling resolution (2 kyr) using piecewise linear interpolation and were detrended from mean prior to analysis. An untuned age model (Lam & Leckie, 2020a) was used to explore external forcing factors that may influence the expansion and contraction of the subtropical gyre system independent of ice volume changes as recorded in the global benthic foraminiferal oxygen isotope stack (e.g., Ahn et al, 2017;Lisiecki & Raymo, 2005;Reilly et al, 2021). Power spectral estimates were made using the robust locally weighted regression spectral background estimation (LOWSPEC), as this technique has been proven to produce substantially lower rates of (Lam & Leckie, 2020b) and Calcareous Nannofossil Biostratigraphy (Bralower et al, 2002) With Ages of Datums Updated to Those in Sutherland et al (2019) false positive estimates compared to other methods (e.g., Mann & Lees, 1996).…”