The dimensions of tubular agglutinated foraminifera such as Rhizammina and Rhabdammina respond

in a predictable manner to changes in the flux of organic carbon to the sea floor. In both the modern

western North Atlantic and in an ancient example (the K/T boundary in Gubbio), the slender,

finely-grained tubes (<100 μm diameter) dominate in oligotrophic regimes, whereas in eutrophic

regimes the abundance of tubes is higher, and the mean and standard deviation of the tube

diameter increases. Large tubes (> 500 μm) are present only when organic flux is comparatively

high. Although our observations are at present not directly calibrated to primary productivity

levels, we maintain that the potential for using tubular agglutinated foraminifera does exist

Kaminski, M.A.

Kuhnt, W.

English

UCL Discovery

    141  In: Kaminski, M.A. Geroch, S., & Gasiƒski, M.A. (eds.), 1995. Proceedings of the Fourth International Workshop on Agglu-tinated Foraminifera, Kraków Poland, September 12-19, 1993. Grzybowski Foundation Special Publication no. 3, 141-144. Tubular agglutinated foraminifera as indicators of organic carbon flux   MICHAEL A. KAMINSKI1 and WOLFGANG KUHNT2 1. Research School of Geological and Geophysical Sciences, Birkbeck College and University College London, Gower Street, London WCIE 6BT, U.K. 2. Geologisch-Paläontologisches Institut, Christian-Albrechts-Universität Kiel, Olshausenstr. 40, D-24118 Kiel, F.R.G.   ABSTRACT The dimensions of tubular agglutinated foraminifera such as Rhizammina and Rhabdammina respond in a predictable manner to changes in the flux of organic carbon to the sea floor. In both the modern western  North  Atlantic  and  in  an  ancient  example  (the  K/T  boundary  in  Gubbio),  the  slender, finely-grained tubes (<100 µm diameter) dominate in oligotrophic regimes, whereas in eutrophic regimes  the  abundance  of  tubes  is  higher,  and  the  mean  and  standard  deviation  of  the  tube diameter increases. Large tubes (> 500 µm) are present only when organic flux is comparatively high.  Although  our  observations  are  at  present  not  directly  calibrated  to  primary  productivity levels, we maintain that the potential for using tubular agglutinated foraminifera does exist.    INTRODUCTION The amount of secondary production at the sea floor is directly proportional to the flux of food particles available  to  the  benthos.  Studies  of  calcareous benthic foraminifera from the equatorial Pacific have demonstrated  beyond  any  doubt  that  the accumulation rate of benthic foraminifera in pelagic sediments  can  be  directly  linked  to  the  amount  of primary productivity in surface waters (Berger et al., 1994), and constitutes one of the best trophic proxies for  organic  carbon  flux  to  the  sea  floor.  Studies  of Pleistocene  cores  from  the  equatorial  Pacific  have shown  that  not  only  were  larger  populations  of benthic foraminifera sustained during glacial stages when primary productivity was higher than  today, but the  mean dimensions  of taxa such as Uvigerina also  increased  (Pederson  et  al.,  1988).  If  this  size increase in benthic foraminifera is a regular feature of high  productivity  regimes,  then  a  simple  count  of benthic foraminifera may underestimate the benthic foraminiferal biomass. Perhaps a more robust proxy for  organic  carbon flux  would be  some measure of benthic foraminiferal volume.    The  Benthic  Foraminiferal  Accumulate  Rate (BFAR) can only be used faithfully under the best of circumstances.  If  there  is  increased  dissolution (which  is  sometimes  the  case  in  areas  with  high productivity),  or  dilution  by  terrigenous  sediments the index must be used with caution. Unfortunately, in the case of the deep sea or in clastic basins where only agglutinated foraminifera are preserved, we are still at a loss to use the BFAR to adequately predict productivity from benthic foraminiferal assemblages.   As a first step towards  defining a trophic proxy for organic carbon flux from deep water agglutinated foraminiferal assemblages, we examined the dimen-sions  of  the  tubular  agglutinated  foraminifera Rhizammina and Rhabdammina from two environmen-tal  settings  (one  modern,  the  other  ancient)  where significant  gradients  or  rapid  changes  in  primary productivity  are  well  documented.  We  selected  the tubular forms because they are abundant in a variety of  environmental  settings,  are  reported  to  be epifaunal  detritivores  or  deposit  feeders  (Jones  & Charnock, 1985), often forming branching networks on the sediment surface or in the fluffy surface layer (Geroch & Kaminski, 1993). Other tubular forms have been observed to be suspension feeders that capture organic  detritus  using  a  spiderweb-like  net  of pseodopodia (Altenbach et al., 1988). They are often abundantly  preserved  in  the  fossil  flysch-type assemblages.  By  comparing  our  fossil  record  from Gubbio  with  the  modern  analogue  of  the  western North Atlantic, we can gain a rough appreciation of the  magnitude  of  change  in  organic  productivity across the K/T boundary.    Material and Methods Surficial sediment was sampled from four box cores collected in February-March, 1990 on board the CSS Hudson Cruise 89038 (Table 1). These four sites con-stitute  a  transect  from  highly  productive  slope waters to the oligotrophic Sargasso Sea, and are de-scribed in detail by Kuhnt & Collins (this volume). Station 027 on the continental slope of the Baltimore Canyon area (off New Jersey) has a high terrigenous influx, and the dark greenish-grey colour of the sedi-ment indicates depleted oxygen conditions below the sediment  surface.  Stations  020  and  016  are  within areas  influenced  by  the  Gulf  Stream  and  its  rings, while  Station  007  on  the  Hatteras  Abyssal  Plain  is situated  within  the  Sargasso  Sea,  seaward  of  any influence from Gulf Stream rings. In this boxcore, the 142  Kaminski and Kuhnt Table 1: Location of HUD-89038 boxcore stations ----------------------------------------------------------------------------------------------------------------------------------- Station  Latitude  Longitude  Depth  Remarks ----------------------------------------------------------------------------------------------------------------------------------- BC 007  33° 41.2' N  57° 38.3' W  4437 m  northwest Sargasso Sea BC 016  36° 00.40' N  66° 05.40' W  4654 m  Sargasso Sea, beneath cold core rings BC 020  37° 31.23' N  72° 00.97' W  3098 m  Gulf Stream area BC 027  38° 44.58' N  72° 29.67' W  2330 m  Baltimore Canyon -----------------------------------------------------------------------------------------------------------------------------------   whole  sediment  column  was  well  oxygenated, indicating low organic carbon flux.    Primary productivity across the transect varies by at least a factor of four. The Sargasso Sea has primary productivity values on the order of 25-40 gCorg/m2y, while  the  inshore  waters  overlying  the  Baltimore Canyon  continental  slope  has  production  values  of 90-180  gCorg/m2y  (Berger  et  al.,  1987).  Because Station 027 is 2000 m shallower than the stations in the Sargasso Sea, a greater proportion of the export production  reaches  the  sea  floor.  The  sea  floor organic carbon flux may be 14-15 times higher than in the Sargasso Sea, if  the flux equations  of Berger (1989) can be confidently applied to this area.    Foraminiferal samples were collected from the top centimetre  of  a  7  cm  diameter  push  core  that  was inserted into the box core. The samples were imme-diately fixed in a formaldehyde/sea  water  solution buffered  with borax and  stained  with  Rose  Bengal. Samples  were  then  sieved,  dried,  and  specimens were mounted onto cardboard slides.    The K/T boundary samples analysed in this study were collected from the  Contessa Highway  section, near  Gubbio,  Italy.  Samples  weighing  exactly  100g were  dissolved  in  HCl  to  release  the  agglutinated foraminifera, sieved over a 63 µm screen, then dried. The  residue  was  then  boiled  in  Calgon  and  sieved again. This process was repeated until no limestone or  clay  remained.  Agglutinated  foraminifera  were picked  from  the  >125  µm  fraction  of  the  dried residues. The length and  maximum width  of every tubular  fragment  was  measured  with  an  optical micrometer.     RESULTS New Jersey - Sargasso Sea Transect  The  distribution  of  size  classes  of  tubular  aggluti-nated foraminifera shows clear differences along the transect  (Fig.  1).  Rhabdammina  spp.  and  large  frag-ments  of  Astrorhiza  spp.  with  test  diameters  above 400  µm  characterise  Station  027  on  the  New  Jersey slope.  Rhabdammina  spp.  with a bimodal  maximum in test diameter at 125 µm and 250-300 µm dominate at  the  Station  020  beneath  the  Gulf  Stream.  At  the deeper Station 016, the dominant mode is at 100-150 µm,  but  there  is  still  evidence of  a  much  smaller               Figure 1. Diameter of tubular agglutinated foraminifera in surface sediment samples from the New Jersey continental slope (Station 027); the Western Boundary Undercurrent/Gulf Stream (Station 020), cold core rings zone of the Sargasso Sea (Station 016), and in the oligotrophic Sargasso Sea (Station 007). Based on measurements of 72 (Station 007); 51 (Station 016); 321 (Station 020); and 205 (Station 020) individuals and fragments. Note that Y-axes are not to the same scale.   Tubes as indicators of organic flux    143  population of tubes with test diameters between 250 and 300 µm. There were no tubes larger than 300 µm. Station  016  is  not  directly  affected  by  Gulf  Stream, but the occasional cold core ring may bring enhanced productivity to the area. At Station 007, which is well within the Sargasso Sea, the size distribution is dis-tinctly unimodal, and tiny rhizamminids with a di-ameter of ca. 50 µm dominate the sample. The largest tubes at this station have a width of only 200 µm.   Cretaceous/Tertiary Boundary at Gubbio Carbon  isotopes  provide  evidence  of  a  world-wide reduction in oceanic primary productivity coincident with  the  deposition  of the K/T boundary clay and during the first few hundred thousand years of the Paleocene  (Zachos  &  Arthur,  1986;  Kaminski  & Malmgren, 1989). The Scaglia Rossa near Gubbio in Central  Italy  was  deposited  under  tranquil  con-ditions  at  a  paleodepth  of  about  2500-3000m (Labude,  1984),  and  deep-water  agglutinated foraminifera are abundant throughout the formation (Kuhnt, 1990). Because all the samples were collected from a single location, we can eliminate any bias in our  tube  diameter  data  owing  to  changes  in  water depth, oceanic currents, or geographical position. We can  be  reasonably  certain  that  variability  in  our faunal  data  reflects  changes  in  trophic  structure related to productivity.    The tubular foraminifera present in the Contessa Section  mostly  belong  to  the  genera  Rhizammina, Nothia, Rhabdammina, and Bathysiphon. In the sample collected from the uppermost Maastrichtian (3-8 cm below the K/T boundary), the 100-150 µm size class dominates.  However,  the  distribution  is  skewed, with a sizeable proportion of the population between 200  and  400  µm.  The  odd  larger  specimen  is  also present  (to  560  µm).  The  cumulative  length  of  the tubes is high (123.29 mm/ 100g).    The basal Paleocene  samples from  Contessa  dis-play  dramatically  reduced  numbers  of  tubes  (the cumulative  length  is  only  6.84  mm/  100g).  In  this study we sampled every limestone bed individually, and  the  data  presented  in  Figure  2  represents  the combined numbers from four 100g samples (2-10 cm above  the  boundary  clay).  The  size  classes  show  a broad peak between 120 and 240 µm, but the size dis-tribution appears to be truncated at 250 µm. Only a single  larger (300 µm)  specimen was found. Signif-icantly,  the  taxonomic  composition  of  this  sample differs from that of the Maastrichtian, with most of the  assemblage  comprised  of  Rhabdammina,  rather than small Rhizammina.    Higher in the Paleocene, a sample collected from 30-37 cm above the K/T boundary already shows the beginning  of  the  recovery  of  tubular  forms.  The cumulative  length  of  tubes  in  this  sample  is  30.53 mm/ 100g). The size classes again show a broad peak between 100 and 160 µm, and the larger tubes (>250 µm) are beginning to make their reappearance. The maximum diameter encountered was 440 µm.   05101520254080120160200240280320360400440480520560012345Width (µm)4080120160200240280320360400440480520560Cumulative Length (mm)101202468Cumulative Length (mm)Cumulative Length (mm)4080120160200240280320360400440480520560Width (µm)1.3-8 cmbelow K/T(100 g)2.2-10 cmabove K/T(400 g)3.30-37 cmabove K/T(200 g) Figure 2. Diameter of tubular agglutinated foraminifera in samples from the K/T boundary in the Contessa Highway Section. Based on measurements of 218 (3-8 cm below the boundary); 56 (basal Paleocene); and 116 (30-37 cm above the boundary) individuals and fragments. Note that Y-axes are not to the same scale.  144  Kaminski and Kuhnt DISCUSSION This reconnaissance study of both the modern North Atlantic and a fossil analogue reveals that both the relative size and total abundance of tubular aggluti-nated foraminifera varies with respect to productiv-ity.  The  highly  productive  area  of  the  Baltimore Canyon  sustains  high  tube  populations,  with  a  bi-modal distribution. In this area, a small proportion of the  assemblage  reaches  a  diameter  of  >400  µm.  In deeper water beneath the Gulf Stream, the tail of the size distribution becomes truncated at 400 µm. In the oligotrophic waters of the Sargasso Sea, the tube pop-ulation  is  sparse  and  the  size  distribution  is  uni-modal, consisting entirely of very small forms.    The distribution of size classes in the uppermost Maastrichtian of the Contessa Valley section is uni-modal  with  a  broad  tail  extending  to  450  µm.  The tube population in this sample has a size distribution that  is  intermediate  between  those  recovered  from Station 016 in the northern Sargasso Sea and Station 020  beneath  the  Gulf  Stream.  Not  surprisingly,  the "Strangelove Ocean" of the earliest Paleocene is mani-fested  by  an  abrupt  crash  in  the  tube  population. Numbers of tubes in the basal Paleocene of Contessa are  one-sixth  of  Maastrichtian  values.  As  expected, the  large  tubes  (>250  µm)  have  disappeared,  but surprisingly,  the  smallest  "Dendrophrya-type"  tubes also declined drastically. As a result, the mean width of those tubes that remain actually shows an increase compared with the Maastrichtian population.     The meaning of this size change is not intuitive, because one would expect to observe a decrease in the  mean  width  associated  with  the  "Strangelove Ocean". However, the basal Paleocene benthic foram-iniferal assemblages are dominated by infaunal mor-photypes,  which  are  normally  present  in  areas  of high organic carbon accumulation. The tubes present are  of  the  Rhabdammina  type,  and  these  may  have been surficial detritivores that lived on the sediment surface  rather  than  living  as  suspension  feeders (Geroch & Kaminski, 1993). It appears that the small, delicate  specimens  of  Rhizammina,  a  form  that  is known to live in the  surficial fluff, were present in much  reduced  numbers  in  the  earliest  Paleocene. Recovery of the tubular foraminifera is evident 30 cm above  the  K/T  boundary,  with  a  return  to  larger specimens  and  a  population  dominated  by  120-160 µm size class.    Although our observations are at present strictly qualitative, we maintain that the potential for using tubular agglutinated foraminifera as a proxy for or-ganic flux does exist. Our initial survey indicates that major differences are observed in the tube population from  oligotrophic  to  eutrophic  areas.  Surprisingly, the  magnitude  of  change  in  tube  diameters  at  the K/T boundary was low in comparison to the range of  variability  observed  among  modern  populations of tubular forms. The key to developing a "paleopro-ductivity  index"  will  be  to  directly  calibrate  tube diameter to primary productivity by the use of other proxy information. This may lead to a valuable new tool for using flysch-type assemblages as indicators of past environmental conditions.   ACKNOWLEDGEMENTS  We  thank  the  crew  of  the  C.S.S.  Hudson  for  their help  during  the  collection  of  the  samples.  Both authors  gratefully  acknowledge  support  from  the Killam  Post-doctoral  fellowship  programme  at Dalhousie  University,  and  from  the  NATO Collaborative  Research  Grants  Programme,  grant number  890149.  This  is  contribution  no  48  of  the Deep-Water Agglutinated Foraminifera Project.  REFERENCES Altenbach,  A.V.,  Unsold,  G.  &  Walger,  E.  1988.  The hydrodynamic Environment of Saccorhiza ramosa (Brady). Meyniana, 40, 119-132. Berger,  W.H.,  Smetacek,  V.S.  &  Wefer  G.  1989.  Ocean productivity  and  paleoproductivity  -  an  overview.  in: Berger,  W.H.,  Smetacek,  V.S.  &  Wefer  G.  (eds.). Productivity of the Ocean: Past and Present. John Wiley & Sons, Chichester. 1-34.  Berger,  W.H.,  Fischer,  K.,  Lai,  C.  &  Wu,  G.  1987.  Ocean productivity and organic carbon flux. Part 1. Overview and maps of primary production and export production. Univ. Calif. San Diego, SIO Reference 87-30.  Berger, W.H., Herguera, J.C., Lange, C.B. & Schneider, R. 1994.  Paleoproductivity:  Flux  proxies  versus  nutrient proxies and other problems concerning the Quaternary productivity  record.  in:  Zahn,  R.,  et  al.  (eds).  Carbon cycling in the glacial ocean: Constraints on the ocean's role in global change. NATO ASI Series I, 17, 385-412.  Geroch, S. & Kaminski, M. 1993. The morphology and sys-tematics of Nothia excelsa (Grzybowski), a deep-water ag-glutinated  foraminifer.  Rocznik  Polskiego  Towarzystwa Geologicznego, 62, 255-265. Herguera, J. & Berger, W.H. 1991. Paleoproductivity from benthic  foraminiferal  abundance:  Glacial  to  postglacial change in the west-equatorial Pacific. Geology, 19, 1173- 1176. Jones,  R.W.  &  Charnock,  M.A.  1985.  Morphogroups  of agglutinating  foraminifera.  Their  life  position,  feeding habits  and  potential  applicability  in  (paleo)ecological studies. Revue de Paleobiologie, 4, 311-320. Kaminski, M.A. & Malmgren, B.A. 1989. Stable isotope and trace  element  stratigraphy  across  the  Cretaceous/ Tertiary boundary in Denmark. Geologiska Föreningens i Stockholm Förhandlingar, 111, 305-312. Kuhnt,  W.  1990.  Agglutinated  foraminifera  of  western Mediterranean  Upper  Cretaceous  pelagic  limestones (Umbrian  Apennines,  Italy,  and  Betic  Cordillera, Southern Spain). Micropaleontology, 36, 297-330. Labude,  C.  1984.  Sedimentology,  subsidence,  and  distri-bution  of  agglutinated  and  planktonic  foraminifera  in the  Maastrichtian  of  the  Central  Apennines  (Italy). Tübingener Mikropaläontologische Mitteilungen, 2, 1-99  Pedersen, T.F., Pickering, M., Vogel, J.S., Southon,  J.N. & Nelson, D.E. 1988. The response of benthic foraminifera to  productivity  cycles  in  the  eastern  equatorial  pacific: faunal  and  geochemical  constraints  on  glacial  bottom water oxygen levels. Paleoceanography, 3, 157-168  Zachos, J.C. & Arthur, M.A. 1986. Paleoceanography of the Cretaceous/Tertiary  boundary  event:  inferences  from stable isotopic and other data. Paleoceanography, 1, 5-26.   

Agglutinated foraminifera of western Mediterranean Upper Cretaceous pelagic limestones (Umbrian Apennines, Italy, and Betic Cordillera,

Morphogroups of agglutinating foraminifera. Their life position, feeding habits and potential applicability in (paleo)ecological studies.

Ocean productivity and organic carbon flux. Part 1. Overview and maps of primary production and export production.

Ocean productivity and paleoproductivity - an overview.

Paleoproductivity from benthic foraminiferal abundance: Glacial to postglacial change in the west-equatorial Pacific.

Paleoproductivity: Flux proxies versus nutrient proxies and other problems concerning the Quaternary productivity record. in:

Sedimentology, subsidence, and distribution of agglutinated and planktonic foraminifera in the Maastrichtian of the Central Apennines

Stable isotope and trace element stratigraphy across the Cretaceous/ Tertiary boundary in Denmark. Geologiska Föreningens i Stockholm Förhandlingar,

The hydrodynamic Environment of Saccorhiza ramosa

The morphology and systematics of Nothia excelsa (Grzybowski), a deep-water agglutinated foraminifer. Rocznik Polskiego Towarzystwa Geologicznego,

The response of benthic foraminifera to productivity cycles in the eastern equatorial pacific: faunal and geochemical constraints on glacial bottom water oxygen levels.

Tubular agglutinated foraminifera as indicators of organic carbon flux

Tubular agglutinated foraminifera as indicators of organic carbon flux

Abstract

Similar works

Full text

Available Versions

UCL Discovery