the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Distinct seasonal changes and precession forcing of surface and subsurface temperatures in the mid-latitudinal North Atlantic during the onset of the Late Pliocene
Abstract. The Late Pliocene marks the intensification of Northern Hemisphere Glaciation, offering a unique opportunity to study climate evolution and ice-sheet related feedback mechanisms. In this study, we present high-resolution Mg/Ca-based sea surface (SST) and subsurface temperatures (SubT) derived from foraminiferal species Globigerinoides ruber and Globorotalia hirsuta, respectively, at the Integrated Ocean Drilling Project (IODP) Expedition 306 Site U1313 in the mid-latitudinal North Atlantic during the early Late Pliocene, 3.65 – 3.37 million years ago (Ma). We find distinct differences between our new G. ruber Mg/Ca-based SST record and previously published alkenone-based SST record from the same location. These discrepancies in both absolute values and variations highlight distinct seasonal influences. The G. ruber Mg/Ca-based SST data, reflecting summer temperatures, were primarily influenced by local summer insolation, showing a dominant precession cycle. Conversely, the variations in alkenone-based SST are found to be more indicative of cold season changes, despite previous interpretations of these records as reflecting annual mean temperatures. A simultaneous decline in Mg/Ca-based SST and SubT records from 3.65 to 3.5 Ma suggests a diminished poleward oceanic heat transport, implying a weakening of the North Atlantic Current. A comparison with early Pleistocene G. ruber Mg/Ca-based SST records shows a shift in the dominant climatic cycle from precession to obliquity, alongside a marked increase in amplitude, indicating an enhanced influence of obliquity cycles correlated with the expansion of Northern Hemisphere ice sheets.
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Status: open (until 11 May 2024)
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RC1: 'Comment on egusphere-2024-603', Heather L. Ford, 15 Apr 2024
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In this manuscript, the authors use the Mg/Ca values of a surface dwelling and subsurface dwelling foraminifera to investigate climate in the North Atlantic during the early Late Pliocene. They find spectral and temperature differences from the existing alkenone-based record highlighting the seasonality in surface foraminifera and alkenones and the related climatological interpretations. I found the use of the subsurface dwelling records to reconstruct the North Atlantic current and poleward heat transporting compelling. I found the study well executed and the manuscript well-written. I have a few minor comments and suggestions to improve the clarify of the manuscript.
Line 122-123: write out abbreviations to full names
Figure 1: Avoid rainbow color palette on figures. You can use BlueRed or Viridis in ODV
Figure 2: Update to ProbStack instead of LR04
Figure 3c: 100 peak blocked by 100 label – adjust position slightly
Line 185: In the last sentence I would reiterative the precession cycle is absent from the 2.4 to 2.8 period, i.e. “The results indicate that the 2.4 to 2.8 Ma records are all dominated by obliquity, with a notable absence of a significant precession cycle after iNHG in comparison to the oNHG (3.3 to 3.7 Ma records)”. The first time I read it and then looked at the figure I was confused so I would just be more specific.
Line 235-240: Do you mean 2000 AD? I would re-write this as “For our study interval (3.65 to 3.37 Ma), the reconstructed CenCO2PIP CO2 concentration averaged around 300 ppm with a maximum value generally not exceeding 360 ppm (Fig. 4c). This is similar to the high-resolution reconstruction for 3.35-3.15 Ma, i.e. immediately following our study period (de la Vega et al., 2020). For comparison, the modern CO2 value in 2000 was 360 ppm. Considering the reconstructed SSTs are warmer than the modern average temperature from 2000 to 2015 (Fig. 1d), the relatively higher CO2 could not be the primary cause of the warmer temperature during the late Pliocene.”
Citation: https://doi.org/10.5194/egusphere-2024-603-RC1
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