//
you're reading...

Paleoceanography

Rapid Reductions in North Atlantic Deep Water during the Peak of the Last Interglacial Period

Article: Eirik Vinje Galaasen et al. Science 343, 1129 (2014); DOI: 10.1126/science.1248667

Introduction

Fig 1. Ocean Circulation

Fig 1. Ocean Circulation

North Atlantic deep water forms primarily in more extreme northern latitudes due to the colder, saltier water with a higher density. When this flow of water goes south it mixes with the cold Antarctic water and then redistributes into other parts of the world (Fig 1). As high latitude warming and ocean refreshing reduce water density, North Atlantic Deep Water (NADW) formation can be prohibited.
Based on model prediction, NADW ventilation is a robust feature in the present interglacial age. Only modest NADW variability has been found during interglacial ages compared to colder glacial ages. We are far from reaching a threshold over which the NADW formation could be stopped. However, large but short transient time may be possible even during a stable NADW forming period, such as an abrupt decadal change within a generally stable millennial-scale period. In these cases, the stability threshold could be crossed and the North Atlantic reaches a steady state wherein no NADW formation happens.

Method

Fig 2. Locations of core sites.

Fig 2. Locations of core sites.

Sediment cores from the Eirik Drift were used to study centennial-scale variability in NADW over the warm interval of the last interglacial period (Fig 2). This period of time helps to understand impacts from key features on NADW including warming, ocean refreshing and the retreat of the North Atlantic ice sheet.

This site is great in that it has the perfect sedimentation rate allowing a long term study of water properties flowing over. It is located in the North Atlantic near the Arctic, where water from Nordic Seas flows.

Fig 3. Deep-water property changes during the last interglacial time.

Fig 3. Deep-water property changes during the last interglacial time.

 

Geographic patterns seen in the fossil records of planktonic forams can be used to reconstruct ancient ocean currents. We use carbon isotopic composition values to deduce values for bottom water. It is an excellent method to distinguish high NADW and low  southern ocean sourced bottom water (SSW). Interestingly, on a short time scale there were several sharp decreases in  (Fig 3).

Fig 4. Proxy records spanning the LIGn(116.1 to 128.0 ky) section of core.

Fig 4. Proxy records spanning the LIGn(116.1 to 128.0 ky) section of core.

Results

These decreases suggest a relationship with freshwater forcing. The minimum value at 124 ky B.P.(before the present) is consistent with reduced NADW production. SSW came in as a compensation for reduced NADW could explain the small value. Furthermore, the increasing anomalies at early stage around 124 ky B.P. shows some links to glacial melting and freshwater input. During forams calcification (Calcium Carbonate formation) some Barium may enter the shell as well due to its similarity as Calcium. By studying the Barium to Calcium ratio we can get properties of the bottom water when shells are formed. Glacial melting water is rich in Barium and causes a higher Ba/Ca value. Around 12 ky B.P. the Ba/Ca value reaches peaks indicating inputs from icebergs (Fig 4). Further supporting a role for freshwater triggering the deep water anomalies, a flood event happened early in the period of study is followed immediately by the largest and longest NADW reduction of the period.

 

Implications

Results from this study call for a reevaluation for the notion that NADW formation is rather stable and vigorous during interglacial time. Sharp changes in short period of time could lead to disturbance to NADW formation, resulting in a change in global heat transport by ocean currents. This causes widespread and long-lasting impacts on our climate.

Discussion

No comments yet.

Post a Comment

Instagram

  • by oceanbites 3 weeks ago
    Not all outdoor science is fieldwork. Some of the best days in the lab can be setting up experiments, especially when you get to do it outdoors. It’s an exciting mix of problem solving, precision, preparation, and teamwork. Here is
  • by oceanbites 1 month ago
    Being on a research cruise is a unique experience with the open water, 12-hour working shifts, and close quarters, but there are some familiar practices too. Here Diana is filtering seawater to gather chlorophyll for analysis, the same process on
  • by oceanbites 3 months ago
    This week for  #WriterWednesday  on  #oceanbites  we are featuring Hannah Collins  @hannahh_irene  Hannah works with marine suspension feeding bivalves and microplastics, investigating whether ingesting microplastics causes changes to the gut microbial community or gut tissues. She hopes to keep working
  • by oceanbites 3 months ago
    Leveling up - did you know that crabs have a larval phase? These are both porcelain crabs, but the one on the right is the earlier stage. It’s massive spine makes it both difficult to eat and quite conspicuous in
  • by oceanbites 3 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring Cierra Braga. Cierra works ultraviolet c (UVC) to discover how this light can be used to combat biofouling, or the growth of living things, on the hulls of ships. Here, you
  • by oceanbites 3 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Elena Gadoutsis  @haysailor  These photos feature her “favorite marine research so far: From surveying tropical coral reefs, photographing dolphins and whales, and growing my own algae to expose it to different
  • by oceanbites 4 months ago
    This week for  #WriterWednesday  on Oceanbites we are featuring Eliza Oldach. According to Ellie, “I study coastal communities, and try to understand the policies and decisions and interactions and adaptations that communities use to navigate an ever-changing world. Most of
  • by oceanbites 4 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Jiwoon Park with a little photographic help from Ryan Tabata at the University of Hawaii. When asked about her research, Jiwoon wrote “Just like we need vitamins and minerals to stay
  • by oceanbites 5 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring  @riley_henning  According to Riley, ”I am interested in studying small things that make a big impact in the ocean. Right now for my master's research at the University of San Diego,
  • by oceanbites 5 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Gabby Stedman. Gabby is interested in interested in understanding how many species of small-bodied animals there are in the deep-sea and where they live so we can better protect them from
  • by oceanbites 5 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Shawn Wang! Shawn is “an oceanographer that studies ocean conditions of the past. I use everything from microfossils to complex computer models to understand how climate has changed in the past
  • by oceanbites 5 months ago
    Today we are highlighting some of our awesome new authors for  #WriterWednesday  Today we have Daniel Speer! He says, “I am driven to investigate the interface of biology, chemistry, and physics, asking questions about how organisms or biological systems respond
  • by oceanbites 6 months ago
    Here at Oceanbites we love long-term datasets. So much happens in the ocean that sometimes it can be hard to tell if a trend is a part of a natural cycle or actually an anomaly, but as we gather more
  • by oceanbites 6 months ago
    Have you ever seen a lobster molt? Because lobsters have exoskeletons, every time they grow they have to climb out of their old shell, leaving them soft and vulnerable for a few days until their new shell hardens. Young, small
  • by oceanbites 7 months ago
    A lot of zooplankton are translucent, making it much easier to hide from predators. This juvenile mantis shrimp was almost impossible to spot floating in the water, but under a dissecting scope it’s features really come into view. See the
  • by oceanbites 7 months ago
    This is a clump of Dead Man’s Fingers, scientific name Codium fragile. It’s native to the Pacific Ocean and is invasive where I found it on the east coast of the US. It’s a bit velvety, and the coolest thing
  • by oceanbites 8 months ago
    You’ve probably heard of jellyfish, but have you heard of salps? These gelatinous sea creatures band together to form long chains, but they can also fall apart and will wash up onshore like tiny gemstones that squish. Have you seen
  • by oceanbites 9 months ago
    Check out what’s happening on a cool summer research cruise! On the  #neslter  summer transect cruise, we deployed a tow sled called the In Situ Icthyoplankton Imaging System. This can take pictures of gelatinous zooplankton (like jellyfish) that would be
  • by oceanbites 9 months ago
    Did you know horseshoe crabs have more than just two eyes? In these juveniles you can see another set in the middle of the shell. Check out our website to learn about some awesome horseshoe crab research.  #oceanbites   #plankton   #horseshoecrabs 
  • by oceanbites 9 months ago
    Feeling a bit flattened by the week? So are these summer flounder larvae. Fun fact: flounder larvae start out with their eyes set like normal fish, but as they grow one of their eyes migrates to meet the other and
WP2Social Auto Publish Powered By : XYZScripts.com